I remember that feeling, a friend of mine has a Citabria (he was also the CEO of Vintage Wings Canada and has owned and flown every warbird you can think of over the years). I've only had one flight in the Cit and one in a Harvard (Texan more or less). I thought all those same things.
If you're young, get your PL as soon as you can swing it, as life goes on, it'll get harder to make either the $ or the time to do so.
I thought the same thing about WW2 pilots, and how exhausting pulling a plane around for all those hours must have been. Those 8 hour P51 missions into Europe and the like. Chuck Yeager wrote a bit about it, and how being in shape was critical - he told a story about fighting a 109 in a circling fight that went on quite a while, and he could always tell when the other pilot was tiring by the moves he made, or lack thereof, and then knew he had them.