mellowing (Noun) — The process of becoming mellow.
mellowing (Verb) — Soften, make mellow. ex. "Age and experience mellowed him over the years"
mellowing (Verb) — Become more relaxed, easygoing, or genial. ex. "With age, he mellowed"
mellowing (Verb) — Make or grow (more) mellow. ex. "These apples need to mellow a bit more" ex. "The sun mellowed the fruit"