Origins
The word 'mature' entered English in the mid-fifteenth century from Latin 'mātūrus,' meaning 'ripe, seasonable, timely, early.' The word came both directly from Latin and through Middle French 'mature.' Its PIE root is generally reconstructed as *meh₂-, carrying a sense of 'good' or 'timely,' though the exact reconstruction is debated among Indo-Europeanists.
The semantic range of Latin 'mātūrus' is instructive. It meant 'ripe' when applied to fruit, 'timely' or 'seasonable' when applied to events, and 'early' when applied to time — senses that seem contradictory until one understands the agricultural logic. In a farming society, ripeness is the ultimate form of timeliness: a crop that matures at the right moment, neither too early nor too late, is the ideal. 'Mātūrus' captured this concept of arriving at the optimal point. The sense of 'early' (as in 'premature') preserves the temporal dimension: something that arrives before its proper time of ripeness.
The connection to time is reinforced by a probable etymological link to the Roman goddess Mātūta, a deity of the dawn and of childbirth, and to the adjective 'mātūtīnus' (of the morning), which entered English as 'matutinal.' If this connection holds, then 'mature,' 'matutinal,' and the goddess Mātūta all descend from the same root, uniting the ideas of ripeness, morning (the 'ripe' moment when night becomes day), and the timeliness of birth.
Latin Roots
'Premature,' meaning 'occurring before the proper time,' entered English in the mid-sixteenth century from Latin 'praemātūrus' (too early, untimely). The word is widely used in medicine, particularly for 'premature birth' — a usage that literally means 'born before the time of ripeness.' 'Immature,' meaning 'not yet ripe or fully developed,' entered English around the same time.
The verb 'to mature' appeared in the sixteenth century, meaning both 'to ripen' (intransitive) and 'to bring to maturity' (transitive). In finance, 'to mature' has a specialized sense dating from the eighteenth century: a bond or investment 'matures' when it reaches the date at which the principal is due for repayment. The financial metaphor is apt — the investment has reached its 'ripe' moment, the time when it delivers its full value.
In modern English, 'mature' carries both positive and euphemistic connotations. Positively, it implies wisdom, developed judgment, and emotional stability ('a mature response'). Euphemistically, it serves as a gentler synonym for 'old' or 'aging' ('mature skin,' 'mature students,' 'mature content'). The euphemistic use, particularly in marketing ('mature audience'), dates from the mid-twentieth century and parallels the euphemistic use of 'adult.'