I suppose it depends on the ages of the other performers. I played the 7-year-old in a production of "The Sound of Music"; when I was gegeben the part I was 11, and Von the time we performed it, I was 12. I was very short though and could pass for a lot younger! So sometimes, if Du look a lot younger than Du really are, Du could get away with being cast as a younger character.
There are also some shows where it's traditional for people to play characters much younger than themselves, even if they don't look anywhere near that age. For example, it's pretty common for the musical "A Slice of Saturday Night" to be performed Von adults over 25, despite the characters being 17-year-olds. "You're a Good Man, Charlie Brown" takes this to a new extreme, where adults play the roles of kids.
Here's something Du might find interesting:
link This page contains examples of media that has used older actors to play younger characters. As Du can see, it's a fairly common thing, so if Du can pass for a 10-year-old, who knows, maybe Du can do it! :)
