There are any number of ways to do this—what works best for you will depend upon what kind of story you are telling, what the narrative perspective is, and many other factors. If it’s important for your story that your readers are aware of the passage of time, you will want to indicate it somehow, but you need not be explicit or heavy-handed about it; it can be implied. You can use your explicit heading approach for the big jumps, and something less heavy-handed for the smaller jumps. Some of the choices include:
* Explicitly stating the date at the beginning of the chapter or scene. This can work in a book that’s framed as a journal or a series of letters, but might be intrusive in a regular third-person narrative. I sometimes find it a bit unhelpful; I can see that the chapter I am about to start is “26 October, 1868” but do I actually remember whether the previous chapter was “25 October, 1868” or “31 March, 1868” or “8 September, 1862”? Usually I don’t. Your age headings might be easier to follow, though.
* Stating the passage of time in the narrative: “Three weeks later, Tom boarded the ship for Athens.” Or, “After a good night’s sleep, Sarah felt better prepared to face her mother.” Or, “There was no sign of him for six months.” Or “It was autumn before Jane found the time to call.” This can work if it fits your narrative style—it can be a little distant, but if your story supports that kind of narrative distance occasionally, there’s no problem with it.
* Implying the passage of time without stating it explicitly. For instance, in the course of a scene, a character thinks about events in the previous scene as “what had happened with Jane last night.” Or, you have a scene that takes place on Christmas morning, and in the next scene your character is cleaning up champagne glasses after a New Year’s party. Or, you have have a character think about or otherwise imply multiple events occurring between the last scene and this one such that a certain amount of time had to have passed, even if the amount is still unspecified. For instance, one scene shows an architect sitting down to begin his drawings on a project, and in the next scene he’s attending the groundbreaking. There are any number of ways to imply the passage of time more or less subtly; these might work best for a close third-person narrative where any explicit statement like “The following week” might feel a little intrusive.
TL;DR — There are myriad ways to suggest the passage of time, implicitly or explicitly; which one is best for you depends upon your story.
