I'm pretty sure early on they said they were between 11 and 13. Or it was said somewhere. I don't think they were all the same years old.
And where I come from, it's perfectly fine for people within a couple years of each other to hang out. It wouldn't have been weird at all. Though I live in Alabama, and it might be different in California. I didn't keep up with ages, and I certainly didn't exclude people just because they weren't within 12 months of my age. If I told anyone that someone couldn't play with me because they were a year or so younger or older, my parents would have thought I was the weird one.
I mean when someone introduces themselve to you, do you ask them how old they are? And then tell them they can't hang out with you in your free time because their age doesn't match up with yours?