It's not necessarily difficult to have age differences in a team: it depends on the people and the team culture.
Notice that iOS development is basically Cocoa, which is basically OpenStep, which is basically NeXTstep, which existed since 1988. Therefore you may very well find people 50 years old and more, who know very well, NeXTstep, OpenStep, Cocoa and iOS, with 29 years of experience developping applications on this platform!
If I had the opportunity to hire such a developer to work with a team of newbies, I wouldn't hesitate, he would be invaluable (and too bad he'd be so close to retirement!).
On the other hand, it may be hard to find them, because they're probably working on their own apps.
In one of my first jobs when I was twenty, there was an old engineer (70+), from which we learned a lot. If you can organize you team such as people are helpful and teaching one another to improve in capabilities and how-to, then having a diverse team, in formation, experience and age is a great way to get a very good team. (and diversity in sex or race just doesn't matter; what matters is formation and experience, and age is only a strong indicator for different formations and experiences, while sex and race are not).