Adult learners of English or any other language can perfectly learn and even acquire the target language.
They have potentials that young learners may not have, like self-discipline and organizing their learning and planning it.
So they have the cognitive and metacognitive resources to learn and acquire. Moreover they have an easy capability of contacting and communicating with other people, a thing many teens or children don’t have – adolescents may be closer to certain gang and that’s it.
The thing sometimes is that adults have to take the resolution of plunging into the water, this is, to break the barrier of starting to talk in the target language.
They have to feel confident and free: I do this because I just want to - which is something that teens are still learning and acquiring. / Photo from: Adult-Group-Talking galleryhip com