I'll be applying next year...err in 8 months...and I'll be >35, married with 3 kids.
I've been warned a couple of times by faculty that it will be more difficult because "we older folks don't have as much stamina" which I find a little insulting, but I understand their perspective. Then again, everyone who is not an OB tells me that it is a really bad move to go into OB because of hours, malpractice, sleep, my gender, etc. which is compounded because of the age issue. I'm not sure if I'm being naive, but I've found my calling so we'll see how much these things really matter, including and in the context of my age.