how big do leopard geckos grow?

Im in Ireland, and i only go to one store for my snake supplies.they do everything there, but they do alot of lizards and mostly corn snakes but,they do look after their animals.they have a 2 people there who are prertty knowledgable about reptiles, and 2 more who are learning quickly.
the other store who dont look after their animals is about 20 miles from me,they had about 10 leopard geckos(babies) in a tank not nore than 15 gallons.
i was thinking of getting one as my neice, even tho she is almost 4, young i know but she loves lizards,she knows more about what they weat than i do even.swhe loves the 4 fish i have and loves when i take the snakes out.(she doesnt handle them but loves to see them move)

The Petco here allows their reptiles hides, especially the snakes. But they have thier ball pythons in one tank with only one hide. :( But the king, corn, and milk snake all have one hide (only one snake per tank) and tons of aspen to burrow into.

Leos are normally skinny at petstores. I've been advised to get one from a breeder, and as much as I'd like to go out tomorrow and pick one up now, I'm going to wait till the reptile show on Sunday to get mine. And if there isn't one there I like, to the internet!

My cousin had a leo when he was younger but he didn't care for it much and it died. :( But basically, from what I've been told, 10 inches and very nice lizards. :)

i am the biggest advocate of bad mouthing petco but today i had to get some stuff for my crested and hell this one was like top of the line each tank was climate controlled seperatley (looked like a breeders set up) really nice but overall petco is a no go for anything reptile. poor little things i feel like buying them all just so they arent soo miserable anymore. (too expensive though lol)