If you put them together, first of all they will mate as soon as they become sexually mature even if they are not full grown so you are going to put the effort of producing fertile eggs on a female that might not be full grown.
Then their is the stress you will put on the two of them...in the wild if they don't want to be near each other they can move away. There's not enough room in a cage for them to do that unless the cage is really huge. Eventually one or both of them will likely suffer health issues and may die.