He's 30, overweight and thinking about joining. Technically yes he is not past the age limit. No recruiter in the world is going to get him in over a recent high school grad.
Nonsense! If the O.P is truly serious & can lose weight/get in shape to meet the Air Force physical requirements, based on his educational experience alone he would be a prime candidate for many Air Force jobs over most "recent high school" grads. Plus compared to all the Armed Forced branches, the Air Force's physical qualifications are the least physically demanding overall as well.