Yes, your high school gym socks are still "perfectly good." After all, they cover your feet … mostly. Except for the hole your left big toe is sticking through. And the threadbare part on your right heel.
Have you noticed that they always look dingy, even when they're freshly washed? And, if pressed, no one could say for certain what color they used to be?
Toss 'em, boys.
The same goes for old underwear, old undershirts, old towels -- anything yellowed, scuzzy-looking or full of holes (this applies to mesh shirts). And if you can say, decades later, "But I can still fit into these! I wore these jeans in high school!" we're happy for you, but we really wish you would get rid of them. Just because you can, doesn't mean you should.
It's a sad fact of life that nothing in life is permanent. Your white T-shirt has lived a good and useful life. It will be dearly missed (by you at least), but it's time to let go -- and make some room in that drawer for a few new things.