1828, "to render social," from social (adj.). Meaning "to be sociable, to mingle" is recorded from 1895. Meaning "to make socialistic" is from 1846. Related: Socialized; socializing. The phrasing in socialized medicine is by 1912.
He never socializes with his colleagues
The old man hates to socialize
The children must be properly socialized
Children have to be socialized in school
Health care should be socialized!