really? i handle any age, if i need to handle them, like i routinely inspect all my leo's once a week, to see if they have any visual problems or injured themselves or something, its unlikely but id rather be safe.
But if little ones need to be handled then they can be handled. but be gentle
This is wrong. Do not follow this if you ever want to handle your leo.
If you wait that long, you're going to have problems introducing the gecko to handling. Start when they're young - it helps them learn that you're not a threat. Just don't handle a leo soon after you've bought it - give it a week or so to get used to its new home first.
Any leo is going to be stressed to some degree from handling, especially when being introduced to it. Don't believe that there's some magical age or length where a leo decides it can be handled. For instance, a wild adult leopard gecko is not going to think you are not a threat.
There are LOTS of threads on this topic, from when to start and how to go about taming the leo, so read up on this after using the search function.