Your son is young and will be one of the youngest in 10th. There will be 19 year olds, even 20 year old post grads. Repeating a year actually would increase chances of getting in, as there are more spots for 9th grade. My daughter is at one on your list. She went as a repeat Junior. Was always one of the younger ones with a summer birthday. She loves being an older one now. If I remember correctly, the financial aid form has a spot where it asks you how much you think you can contribute. If you need a small amount to make it work I don’t think that would hurt the application. Good luck.