First some good news.. in the next few years he may start doing after school and weekend jobs that will go a long way in helping him overcome these problems. At his age i started working with my much older brother in general house repairs and spruce ups. Every tool he used had a special place both in certain tool boxes and those boxes in the van and trailer we hauled and in the triple garage we built to hold everything. (His kids that gave his eulogy said that was because he bought 3 of every tool) This started me on my recovery to be able to find my own things most of the time. 5 years in the army helped as well.
Somewhere in this process i learned to trace my steps usually but not always from entering home and then follow until I found the mislaid object. This worked more often than not but the habit never completely left me. It returned in spades when Casual Fridays turned into casual everyday at work. I missed those 5, 6, or even 7 pocket suits and sportscoats as I had gradually learned not to put things down that could fit in a pocket.
Now for the bad news….it gets worse after the age of 40. Just about the time the kids are leaving to go to university and the pressure eases up I found myself back in that terrible habit at home.
Now that i am in my 70s i am probably the duplicate of him for losing things. I have however learned to laugh and not blame my daughter who used to borrow all the things i had at the lake while they completed their cabin. I know they will show up. Meanwhile every surface in my home has things i put down until that day i lose my patience and have a massive put away or throw out event. Great feeling of accomplishment when its over.