If there was no one immature in this world, the word of " maturity " would have never existed. Because immaturity is the root of maturity.
If someone thinks that they are immature just because of some of their weaknesses, so being weak doesn't mean that they are immature. It means that they should try it again and again in order to get it improved and to get rid of the fear of not being able to do something.
Whereas, being mature means to be experienced about the obstacles of life and to think smart about it.
Even if someone is immature so they should be glad for that because a person only becomes mature if he's immaturefromthebeginning.