sow one's wild oats - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Behave foolishly, immoderately or promiscuously when young, as in Brad has spent the last couple of years sowing his wild oats, but now he seems ready to settle down. This expression alludes to sowing inferior wild oats instead of good cultivated grain, the verb sowing—that is, “planting seed”—in particular suggesting sexual promiscuity. [Mid-1500s]