I am very into poker as a lifestyle, a world view, so take this for what it's worth.
I think it's good for them, any age. It teaches them a type of high level thinking they don't get in school. Done with proper guidance and a clear understanding of ethics and honest play it can give them life changing insight into a sort of poker world view.
Of course at age ten it's for candy or pennies. Teens can easily get carried away so parental guidance is a must. Zero tolerence for cheating, going outside what is allowed stakeswise etc... has to be enforced. but that is part of the ethics and honor training that goes with. (Which I absolutley abide by) Also teaches them the difference between gambling and skill games even though it can be both.
I have to admit my son who will be 18 in the fall has played on and off for a couple years. In some ways he was a natural; much better than me & he wouldn't pick up a book. At least it got him off the video games for a while.
His motto "I may not have the nuts but i've got the balls" :bootyshak
Goldog