No it is not normal for a true 9th grader to turn 15 during the summer. If he turns 15 after the 1st of Sept then he is a true 9th grader and time before that he is a hold back.
Wasn't always SEPT 1 In fact the rules changed mid way thru last year. Cut off was Mid May - Rule changed well after teams held try outs. This would not even be a topic if that rule did not change. It will change again too.