Aus',
Well, the way stars age is rather more complicate than what you mention, but you're right: it'd be nice if Celestia could eventually include ways to show all the stars aging appropriately.
Right now the only way to do is with the new Beginning and Ending directives in .SSC files, replacing their surface textures over a long period of time. Doing that for a few example stars might be a fun project for someone. (hint, hint).
It'd take some research, of course: learning about the Hertzprung-Russell diagram, ratios of masses to evolutionary rates, etc.