I don't think environment really plays much part into it. I'm one of 5 kids, my sister, who was quite a bit older than I am (7 years older) shared my room. She was somewhat clean. I was not. My younger brother is clean to the point of possible OCD on some things, others he could care less. My other brother had science projects growing in his room. Mom kept the house pretty neat, and we were always being told to clean our rooms so she DID try. Of my three kids, 2 are kinda messy, one is semi-clean. He tries anyway, but when it comes to their clothes none of them can keep a drawer straight.
I always used the excuse that messiness was a sign of creativity, and I never had trouble finding anything, because it was all laid out in front of me

Today I have "stuff" but my house is not dirty. It is somewhat cluttered but 3 kids plus baby on the way just makes life a little chaotic. The worst room is my spare bedroom, which doubles as my sewing room/storage room for all DH's military gear.
18 years of military gear, 2 branches of service, in 3 climates=alot of crap. I have a closet full alone of nothing but various uniforms for desert, woodland, army, air force, etc. plus a few extras he's picked up, and thats before you get into all the bags, pouches, vests, boots, and gadgets. He's a self-professed gearhead, and it clearly shows. Couple that with all my fabric stash, 3 sewing machines, and enough camo fabric to choke a horse spread out (making my baby's bedding) and its quite scary in there!