Hi, I am not young (by your standards)--I am 49 but have been wearing retainers for 30 years! The best way to clean them is to get a denture cleaner with stiff bristles (kind of like a funny looking little toothbrush only it's for dentures). Scrub the heck out of that retainer every day with toothpaste and that will get the plaque off and leave it smelling nice.