Their teeth can many times relay whether a bunny is younger or senior. Senior bunnies normally have much yellower teeth. (and of course they have to put them in glass of water at night…HAHAHA!) Anyway, the white vs yellow teeth doesn’t give you alot to go on. I mean under five or over five is easier to determine – but the in-between is hard to know for sure.
I know that when I went bunny bonding at SaveABunny, the owner clued me into body and face structure for “younger bunnies” – 2-3 years old as opposed to older bunnies. I never actually noticed these differences until she showed me. Their bodies a bit leaner, more muscle, less fat, and unless the breed has a wide face, the face structure can be leaner-looking as well. (though young bunnies can get fat too). However, I must say the only reason that I could notice this rather slight difference was because I saw so many bunnies all at once, I wouldn’t have been able to see the difference. So it helped that I had that opportunity.
Also, energy level can indicate age as well (as long as the bunnies are healthy). My experience has been that bunnies under three years old have lots of energy, like to get into trouble, and then as they reach five years, they seem to mellow out a bit more, less destructive, and then over five, they enjoy lounging more than bouncing around. They will still get up and play, but it better be for a good reason.
Now that is MY experience with my own bunnies and what I have learned from the shelter, but I also know there are exceptions.