“Sowing wild oats” isn’t about sex (though it can be used like that) but rather about the folly of youth. Wild oats don’t need sowing (they’re wild!) but are hard to distinguish from cereal oats. “Sowing your wild oats” means you’re using your time in a foolish way associated with being young and inexperienced/reckless/inattentive.
Example:
“In my youth I thought I’d make a living as a DJ. Dad tried to dissuade me but mum said I had to sow my wild oats.”
