Both have relationship woes, and both are famous for them.
Quite a bit of their songs are both about failed relationships.
Case in point, Adele got pregnant with the boyfriend now husband very early in their relationship.
I guess, if you do compare the content of their songs and their audience, fine, you can make a case that Adele is the more "adult" talent. Otherwise, in regards to their personalities and actual maturity, I wouldn't go there.