I would imagine that they would be in their late teens or early to mid twenties. Except for Celestia, obviously, since she's thousands of years old and immortal.
I found it entertaining to watch when you're with someone else, but otherwise it feels pretty dull to me. But that's just me. That anime is technically a "classic" so it's up to you.
I once remember having an entire conversation with two people for like an hour and the only word they would say is meow and they would play charades. I'm terrible at charades. Wasn't much of a conversation XD