Can braces straighten teen just as easily when you are over 18 years?

Not "as easy...": But braces work at any age. The younger the person, the softer the bone.

Braces: Its never too late but it can be easier the younger you are in age. It'll be worth it.

Yes, but...: I assume you are asking about dental braces. Orthodontic treatment works best when we can harness growth, therefore at the tween-teen interface. The older you get, the more complex the problem becomes, the less growth there is to work with, the longer treatment will take, and there will be a slight negative gradation of the prognosis and a longer retention component after active rx.