Dematured
to have ones self maturity take reverse action and become less mature as a whole
When a man decides to take up video games as a occupation at the age of 40 with three kids and a wife has dematured.
Demature
An individual who gets less mature with age
Based on my behavior at that party last night I have dematured. Normally I only do a keg stand, but this time I decided to shot gun, funnel and keg stand in the same night.