In the US system, the usual path involves a four-year Bachelor's program, a two-year Master's program, and then a two/three/five-year Doctoral program. (My Dad got his Master's and PhD in four years, total, in Aerospace Engineering. There were other people who had been in the doctoral part of things for eight or ten years. They call those people professional students. Many of them don't intend on graduating-- they're happy being students, they like being qualified for cheap student housing, they like collecting degrees and certificates, and/or they aren't in a hurry to run out into the real world.)
Whether or not the four years of undergrad (the Bachelor's program) are completed in four years depends on the student. A full-time student should be able to take that number of credit hours and graduate on time. But there are extra circumstances that can make that harder-- like suppose you double-major. Suppose you fail a class and you have to take it twice. Suppose you try to earn a minor while you're at it. Likewise, there a way to accelerate things-- like suppose you transfer credits from a community college, that were either earned during your high school years (dual credit) or over the summer while you're at home. (You only transfer classes that are required for your degree, but not your major-- so you can transfer, say, Inorganic and Organic Chemistry, so long as you're not in a hard science-related field. Or you can transfer French I and French II, as long as you're not a language major.) So there's lots of things that will affect your age at graduation.
Moving on to your Master's, which is a graduate program, suppose you had your undergrad (Bachelor's) degree in Archaeology and Anthropology. Or Archaeology and History. Or Archaeology and Museum Studies/Museum Science. Or Archaeology and Classics (Latin + Greek). At my school, they required students in the Archaeology program to double-major, so students would pick whatever was most useful for their ultimate goal.
However, there's also the rule of thumb that you don't earn your Master's and PhD at the same school that you earned your undergrad at. The classes/lectures are pretty much the same between the BA and the MA-- just the grad students had a lot of extra work on top of it. But it is normal to get your Master's and your PhD at the same school, because the two programs build on each other, and they like to know their doctoral candidates have a particular framework to build on. However, if a lot of time has passed between someone earning their Master's and wanting to pursue a doctoral degree, there's nothing that ties them to the school that they earned their Master's at... they can apply anywhere. But if the two events were closely related in time, it's a whole lot easier to just move on up since you're already in that environment. If too much time passes, however, you lose your "student brain" and it gets hard to get back into the rhythm.
Occasionally, people want to take supplemental classes, but aren't in a program. If it's something like "Introduction to B&W Photography" or "Intro to Watercolors" and has no formal relation to their actual degree, those are generally considered "Continuing Education". They're classes that people take for their personal enrichment, but aren't necessarily as rigorous, and they may or may not have an interest in applying that information to their "real" work. Likewise, if someone takes additional courses, without actually trying for an actual degree, that would often be considered pursuing an "Academic Certificate"-- like, say, 12 hours of extra coursework might result in an academic certificate in Applied Anthropology, or Archival Management, or whatever your student might think would look good on paper, without the time commitment of a full degree.
Because ultimately, that's what a degree is-- it's a key that unlocks a door. So your student needs to figure out what door he wants unlocked, and then undertakes the coursework that would allow him entry into whatever field. You need to figure out why he's pursuing advanced degrees, because Archaeology (and Classics. And Museums. And Anthropology. And so on...) is not a well-paying field... and there's a lot you can do with just a Bachelor's. So you need to figure out what someone wants to do that makes the extra time and financial commitment a wise investment. Full-time in a Bachelor's program is 15 credit hours/semester. Full-time in a Master's or Doctoral program, however, is 9 hours/semester. (I had no clue why I could manage 21 hours my last semester of undergrad, but was struggling with 12 for my first semester of Master's work! Guess what my advisor forgot to tell me!)
Being a student, especially at the doctoral level, is a job. If they're not paying you to go to school at that point, you're doing it wrong...!
For example, when I was a Museum Studies/Archaeology student in Undergrad, I spent one semester working in Oral History, and six semesters working in Collections in our campus museum. It was just a minimum wage thing, but it gave me Experience That Looks Good On Paper, and I was able to leverage that when I graduated. We didn't have a doctoral program in my degree, but if we did, they would have been Teaching Assistants, would have graded papers, would have done some lectures, and so on. Your student is going to be very conscious that the piece of paper unlocks doors, but ultimately, it's just a piece of paper. It's experience that people want to see. So your student is going to want to get experience that makes him look like he knows what he's doing in his field, rather than just having sat in a chair for eight years, listening to people talk. (Can he do an STP Survey? Can he walk 10 miles in a day carrying 40 lbs of equipment? Does he know his way around Trimble? Can he talk for fifteen minutes about the importance of Data QA/QC? Is he familiar with his Munsell Soil Chart?)
A lot will depend on whether your student is married or unmarried. If your student is unmarried, and his parents live close to campus, it would make financial sense to continue living at home. Me, I was married, and my husband was pursuing his JD while I worked on my MLS. We both worked full-time during the day. He went to the night program (which was tailored to People With Jobs and Experience and Wanting a New Direction in Life, whereas the day program was tailored to Bright Young Things Fresh Out of Undergrad), and I did WebCT, with a few electives that I chose to travel up to campus to take in person. About half the librarians in my program earned their degree through WebCT because we had real life going on... and that was more than 15 years ago, so I'm sure the numbers have gone up since then. We graduated with no debt. A friend of ours took out about $100k in loans, and lived off that while she earned her JD... it paid her bills, covered her house payments, etc, and she graduated with... $100k in debt to pay back. She did it just fine and is a very successful corporate attorney, but failure was not an option.
Archaeology is not a well-paying field. In my part of the world, you can expect to earn about $15/hr doing fieldwork with a BA, so that's not the kind of thing you'd take out a $100k loan to do. Many of the fieldwork jobs are seasonal in nature, or even shorter-term than that. It involves a lot of travel, so it's not conducive to putting down roots in a particular location. If you get into things like desk jobs-- archivists, historians, museums-- then you might have expectations in the $30k-$60k/year if you're attached to a very thriving institution. The rule of thumb is you don't want to spend more than 4 years in one place before leveraging yourself into a better position elsewhere. Archaeologists who are at the doctoral level are probably mostly interested in getting into academia.
