Celestia is ancient at this point. We don't have an exact age for the sun princess, but she's been a round for a long time. Unfortunately we only ever really got a few episodes about her general life, with her daredevil antics on her time off with Luna and a few nuggets spread throughout other storylines in the show.
What does she do for fun when the cameras aren't rolling? Do you think she has any weird collections? Or is she so busy with princess stuff she never has time for anything else?