What percentage of the population is "young and strong"?

When various topics dealing with performing or surviving demanding physical feats are discussed, I often hear of such-and-such being decribed as “likely or possible if the person is fairly young and in good shape”. This got me wondering just what the odds are of a random name in the US Census books being such a person.

You wouldn’t expect a 60 year old woman to be able to hoist a 160 man on her shoulders and run over a 1/4 mile of rough terrain to get them to safety, nor an 8 year old boy to survive a cougar attack unarmed. So what percentage of say the US population falls into the 17-40 age bracket and is in good shape …(good enough to succeed in the two examples I gave)? The closest I’ve been able to come is that maybe 15% of the population are males from 20-40; but the percentage of near-athletes in that group has evaded me.

Males vs females is tricky - both those things require a good deal of strength as well as being in good condition… so I’ll leave that open.