Don't be upset if you don't get as many as he said he's write.
Being in Basic is a very hectic life for awhile.All they do is wake early, school,eat,workout,study,clean the barracks and yard,shine boots,etc....He's so tired at the end of the day he can barely see straight.The Marines own him and his time now,so he won't have much, if any free time.
Ask him in his letters to describe his daily routine.I bet you'll be shocked at what all he does in the hours in his day.
Tell him thanks from me for him joining and protecting me and this country.
My hat's off to all the young men and women serving.