It would be weird to have kids with someone who is effectively 20 years younger than you, though.
You either go with someone physically the same age who is of a completely different generation from you, or you go with someone mentally your age who you may not be able to have kids with without risking a higher chance of congenital disorders.
For your first 20-40 trip, you could stay childless and live it up, see the world.
Then, on your second 20-40 trip, you could have kids while still physically fit and able to keep up with them and have fun.
It would be weird to have kids with someone who is effectively 20 years younger than you, though.
You either go with someone physically the same age who is of a completely different generation from you, or you go with someone mentally your age who you may not be able to have kids with without risking a higher chance of congenital disorders.