Older and younger gecko housing problem...?

I have a 4 year old leopard gecko, and i want to place a younger or = age gecko in the same tank 1/2 the time would doing so make the younger gecko, to put it simply die? what should i do? i am going to purchase another tank to put the younger gecko in, but i thought that it would be good for it to be with another gecko. From pryor experience i have found out that if the geckos are to far apart in age that the younger one will die... so begins the delema...