DD 12 is getting along fine, each year better and better, socially. She is in the 8th grade, in a district with a Sept cutoff. So she is essentially 2 yrs younger than most kids in her grade, yet is thriving. She is not the easiest kid to get along with ... really misses nonverbal cues a lot (always has). But she had that problem before she was grade-advanced. She is not allowed to date, but can talk with boys on the phone or IM. She knows that in 2 years, her friends will be able to drive and she will not. Will that cause problems? Doubt it. I could not drive until I was out of high school (parental decision) and I was fine. Didn't even get made fun of. She'll be fine too.
About physical maturity (not referring to any specific post, btw) ... puberty doesn't occur at a magic "age"...you should see my 12 yr old niece. She looks 22. Really. Several of dd's friends, at 14, are not looking any more developed than dd12. I was a late bloomer, my sister early. So I don't think physical maturity will be as big a deal, really, unless it is an extreme difference.
I am just rambling. Need to go bow to the coffee grounds!
Beth