I'm a little unclear on what you're asking here - Born in the early 70s or a teenager in the early 70s (and therefore born in the late 50s).
I was born in 1964, so I was a teenage boy in the late 70s/early 80s in the UK. Strange as it may seem, I don't think teenagers are different mentally or emotionally now to then - only in surface details. Obviously the music, fashions were different.
How did I dress? When out of school uniform, pretty much the same as I do now casually - T-shirt and jeans. Those who went to nightclubs/discos might dress up a bit more, but I was never in that crowd.
Music? Punk was big in the late 70s, but there were always plenty who weren't into it. I went to a Catholic boys' school, so this may distort things a bit. Prog rock was big (Rush, Marillion, both just starting). Quite a few into heavy metal (the famed New Wave of British Heavy Metal, or NWOBHM for short). Other than that, the more musicianly chart rock music, such as Dire Straits (Love Over Gold was a big album, in fact the second one I ever bought). What was NOT cool in that school was anything that girls tended to like, so out were Duran Duran, Spandau Ballet, any of the New Romantics, and most of the synth duos from the early 80s - ESPECIALLY Soft Cell, with their openly gay lead singer.
Being gay was NOT cool, and there was a lot of homophobia around. Someone in my year who was very effeminate had a very hard time. This was made worse when AIDS first become public knowledge (1981).
By the way, I bought music on vinyl then, moving on to cassettes later. CDs didn't come in until the mid 80s. I was swapping Beatles and Dylan albums with friends on tape. I'd say for anyone with a serious interest in music (rather than just listening to what was around on the radio) it's much easier to find stuff now. If there's a track I haven't heard before but would like to try out, nowadays the first place I'd look would be Youtube. Back then, short of blind buying a single or an LP, you had to wait until something turned up on the radio. In the early 80s, a big show for me was Anne Nightingale's request show on BBC Radio 1 on Sunday nights - I heard a lot of great stuff on there. The singles charts were much more essential then than they are now.
What did I do for fun? People were much less paranoid about letting kids out of the house then (even so, we all had warnings not to talk to strangers etc). I tended to be a loner outside school, but I read a lot, went to the cinema, listened to music...which I still do!
Incidentally, home video didn't start until the end of the 70s, and many households (ours included) didn't get a VCR until the mid 80s. You watched films in the cinema (which often came back a few months later, sometimes in a double bill) or you waited five years for them to turn up on TV. Certain big films' premieres on TV were far bigger events than they are now.
There were only three channels on British TV until Channel 4 started in 1982, a day I remember vividly. Back then, there tended to be BBC1 households and ITV households, as to which of the two mass-audience channels you tended to watch. (We were a BBC household.) BBC2 was a minority-audience channel. TV was a family activity, especially with drama series and comedies in the evening - it was unusual to have more than one set, unless the second one was a small portable, which we had in the kitchen. "The Young Ones" was big with older teens when it was first broadcast. As many people didn't have VCRs, you watched the programme when it was broadcast, or on a repeat, or not at all. Back then, in Britain it was an assumption that British TV was superior to American TV which with a few notable exceptions (such as M*A*S*H) was thought rather trashy, and there was more of it on main channels in prime time than there is now. (Nowadays of course, it's a common assumption that the best US television leaves British TV for dust - which is a bit unfair on the best British TV.)
Also, TV was more censored then than now. There was a 9pm "watershed" after which programmes might not be suitable for children. Sex and nudity tended not to be problematic, but strong swearing was out, and that was a taboo that didn't start to be broken in scripted drama until 1979/1980, and films almost always had strong language cut. (Channel 4, which started in 1982, was a pioneer in leaving films and TV shows uncut. I'm not counting certain notorious examples of swearing on live TV such as the Sex Pistols on the Today show in 1976.)
In my later teens, there were boys who had girlfriends and were almost certainly sexually active. In my last year at that school (1982-83, when I was eighteen), the head girl of the local Catholic convent school was pregnant.
This is obviously a UK perspective (I'm sure fashions and trends were different in the USA and elsewhere) but I hope it's of use.