Those awards also apply to adults; so if you just turned 18, sure keep them on.
However, if it’s been a while before you conquered that mile swim, let me throw down a challenge … Are your certifications up to date? Are you doing a mile swim every year? Still snorkeling? How about going for PADI?
As adults, we are expected to up our game and stay fresh. It is really humbling when your aquatics director is half your age and holding that stopwatch while you’re sprinting to recertify BSA Guard. And it’s not just a challenge from aging. Getting old raises the bar a tiny bit. But life demands so much of your time that it is serious work carving enough out your schedule to stay trained so that you are prepared to step in as a guard wherever one may be needed.
Bottom line: if those patches still reflect your current ability to cover distance, dive deep, and forestall death, wear them with pride. If there’s even the slightest doubt that you can do those skills in the nearest body of water right now, take the patches off your shorts, hang them on the mirror, get back to class, and prove yourself anew.