What do you call a person (not merely a young one) who seems to be easy to influence. Someone who others can have their own effect and impact on them in many aspects of their lives:
He is a very impressible person.
He is a very impressionable person.
He is a very susceptible person.
He is a very malleable person.
Based on above links' definitions, you'll see that they can indicate this message about someone, but which one can be used in common and everyday speech? (Of course what I am looking for in my own language is considered a formal word too, but most of the people would understand it even not well educated people.)