It can be done, but it requires the right supplies and preparation. I did it back when I was 25ish and in marathon shape. It was tough but doable. No way I could do it today.Me and two friends, also in our early 20s, found this out as well.Myself and 2 friends found this out the hard way in our early 20s. We made the trek down to the Colorado River and back up and out in one day. Would not recommend.
I was also with a group of people that had done down/back in a single day before, so we were prepared as a group. We started down at daybreak. I think each of us had a camelbak backpack with 2 gallons of water and lots of food. We rested for an hour or so at the bottom, made sure we had plenty to eat and drink. Coming back up is definitely very hard, fortunately we came back up a trail that was shaded for significant portions. You would definitely not want to come up the path we took down, as that was full sun in the afternoon. My feet were pretty beat up when we were done, but otherwise made it no problem. Even then, it probably wasn't a smart idea and I wouldn't recommend it. I'd simply say, if you are going to attempt it, bring lots of water and some snacks.