Anybody felt the same?

On another re-watch, I have noticed how young Angel and Spike looked like, and as the series progressed, on each successive re-watch, I never noticed how they aged (especially when I get to S5 of Angel)

Until of course I go back to Season 1 and notice the change.

Particularly David Boreanaz as he gained in muscle size as the series went on, whereas he's pretty lean in Season 1. (Whereas James Marsters stayed pretty much the same, except for noticeable lines)

The make up department definitely can only do so much, as they're only actors and much as they try, definitely cannot hide their aging.

Not a complain or anything, just a mere observation, I don't know what kind of psychological affect this is (not seeing the actors age as we keep watching the show, and only noticing it through rewatching earlier seasons) and I simply find it interesting and would like to know if any body else noticed it too? Thoughts?