Is a bmi of 19.4 ok for a 5' 1 13 year old boy?

Well my bf weighs 107 and he is 5'5" and 13, but he also has muscles, like a 4 pack so that will give weight! But he is in Excellent shape. So if you weigh 107 or less and your 5'5" 13 year old boy, than you have an amazing body! :)