Back Pain while walking related to low hanging testicles?

Hi.  I feel slightly uncomfortable about asking this, but maybe you men can help me.  I am 43 while my boyfriend is almost 58.  Over the last many months, I've noticed he has been walking with his legs spread out.  His torso bobs from left to right while he is walking.  He hasn't complained of his testicles hurting but he is having back issues.  He started walking up to 10 miles/day about a month ago.  Last night, we were at an outdoor concert and several times, it looked like his knee gave out but he said it was his back and he couldn't walk well... then it would be fine and then happen awhile later. I am wondering if this back pain is possibly being caused by him walking the way he is. I tried offering this theory to him suggesting he change to tighty whities, but he said no that's not it.  But I just can't help but to wonder.

Thank you for your thoughts.