Under Armour Boys' Pennant Tapered Pant

I purchased these pants in black and grey for my grandson for Christmas. Basically just replacing some that he has outgrown because for the last 2 years these are the only pants he will wear. He is thin and these have always been a good, comfortable fit for him. They wash and dry very well. He is 13 and starting to grow like crazy so I am a little concerned that the length won't fit him very long. There is hardly any length difference between the large and the X large. They just seem to be bigger in the butt area and he definitely does not need that. I considered going to an man's small but they are wider yet, so not sure what we will do when he outgrows the length. Under Armour should consider making the lengths a little longer. They have the band on the bottom so the shorter kids could still wear them. I have noticed that other brands are longer in the same sizes.