If you are over 10, you have played with a ball mouse. They're fine until about a year after you buy them. It was a pain to clean them with rubbing alcohol though. Wireless optical mice are a godsend for me because I use a gaming laptop.
Over 10 is pushing it. I figure most kids haven't done much PC video game playing prior to being at least 6-8, and even that's probably a little low.
I don't know about you, but haven't even seen a ball mouse in the last 6 years, let alone played games with one, and don't know any 12 years with fond memorys of age 6 Starcraft sessions with their old ball mouse.
15 is probably a better number to go with. I'm 22, and while I remember having the ball mouse for quite some time, I'm a little fuzzy on actually using it with video games.