The first one is correct, though there should be minor tweaks—you need to put "years of age" after "20" to clarify what you intend to say.

You are thinking Portuguese/Spanish: es posible hacer../fazer? In English we always (?) use the pronoun next to the verb , i.e. he/ she/ it/they, etc. Is IT possible to learn a new language after (the age of) 20? Many people on Italki do that. I've learnt 2 new languages after being 20 years of age. Is it possible ....? Are you ready to ....? Is he coming too? Will IT be possible that....? etc. We need to say 'who' is doing the action. No es posible decir diferente. Disculpe.