Maturity (n.) is a process characterized by a series of energy displacements or object substitutions whereby the source and aim of the instinct (i.e. Oral pleasure) remain the same when the energy is displaced (into smoking, kissing, etc.).
Maturity (n.) is, as the psychic development of the individual, a short repetition of the course of development of the race.
Maturity (n.) is learning to give up momentary, uncertain and destructive pleasure for delayed, restrained, but dependable pleasure.
Maturity (n.) is the ability to postpone gratification.
Maturity (n.) is learning to exchange an immediate yield of pleasure for a surer if postponed one — the advance from the pleasure principle to the reality principle.