It's about gardening, yards, flowers, trees, bugging things, tree rats, grandkids, graduations, birthdays, what the neighbors are doing, what's new, what's old, who's old, how much vodka is needed to impair judgement, how Larissa learned all her great tips, I could go on and on but . . . .
Maybe you'll have better luck with this: https://www.operationgratitude.com/writeletters/
I imagine that when your military penpal gets out, he/she will be happy to meet you for coffee at Denny's.