Adverse possession wouldn't work in this case, because the op neither "posseses" the property, changes it significantly, or is hostile to the owner. The OP would be a tenant as far as the laws are concerned.

Legally, he doesn't have a leg to stand on. He's of legal age where he lives, and if the he doesn't own the house, the owner of the house can charge him rent.
Even if the owner is his mommy.
If you ask me, my original comment reflected the an excellent and responsible stance. The stance of TANSTASFL, or "there ain't no such thing as a free lunch." Someone has to foot the bills, be it medical care, food, clothing, housing, transportation.
As for sqautters rights, here they have none.

I had to delete a few posts, and then there are some others in here that are either of questionable taste or questionable advice. So I will lock it.

OP, I hope you can work something out with your parents.