As a kid growing up in the '80s/'90s, I remember reading a blue hardback book that was a collection of sci-fi space stories. One of the stories I particularly remember ended with the two spacemen finding and drinking from the fountain of youth. They take too much and end up as babies draped in their adult clothes. There were other stories in the book; perhaps involving Vikings but this one is most vivid in my memory. I've been searching on and off for years so any ideas would be greatly appreciated.
I wonder if this could be an excerpt from Charlie and the Great Glass Elevator, which features space travel and pills that reduce Charlie's grandparents to babies (and eventually to negative age).