This site gives the following definition:
1.a. Having reached full natural growth or development: a mature cell.
b. Having reached a desired or final condition; ripe: a mature cheese.
2. Of, relating to, or characteristic of full development, either mental or physical: mature for her age.
3.a. Suitable or intended for adults: mature subject matter.
b. Composed of adults: a mature audience.
4. Worked out fully by the mind; considered: a mature plan of action.
5. Having reached the limit of its time; due: a mature bond.
6. No longer subject to great expansion or development. Used of an industry, a market, or a product.
7. Geology: Having reached maximum development of form. Used of streams and landforms."