5 years old is not that old either, chins can live 15-20 years or more. My guys got their first wheel when they were around 3 (when I got them). Keep in mind that not only do you need a solid surface metal wheel it also needs to be
at least 14", ideally at least 15" especially if the chins are on the larger side. Anything less then that will bend their back wrong and cause back injuries over time, their backs are not designed to bend backwards like other rodents. Also those metal
wheels with spokes are not safe either, they can get feet, legs, tails, and necks broken in them.
Chin safe wheels include the
silver surfer,
the chin spin, and the
metal flying saucer (standard or large size). The flying saucer does have much more of a learning curve then the others though, and some chins can't figure them out. My guys got theirs at around 5 or 6 (can't remember) years old and it took them less then a day to figure it out.