You could definitely house them separately. If you're planning on putting them together, it's a good idea to have another enclosure ready anyway in case they don't get along.
the pet store said if the gecko that i have now wasnt born with another gecko and raised together i cant buy another one and put them in the same tank. and i have 2 backup tanks
oh OK, that doesn't sound right i bought 2 geckos from 2 separate pet sores and i housed them together for a while until Cleo wasn't gaining wait then i separated them.
Yeah, pet store is wrong. I move my geckos around all the time. But only the females. I house a group of girls together for awhile before I introduce their male for the season. Sometimes there are personality conflicts, but mostly if there are enough hides (including lay chambers) everyone gets along okay.
The main problem you might have is ending up with two males. They will fight. And unless you plan to breed, you really dont want a male and female housed together.
So plan carefully, or wait until yours grows up and you know their gender.