Chassidish boys often get married at 18. Sometimes even younger. 20 is already almost a late age for a Chasidish boy to get married.
The Chasidish 18-21 year olds aren’t more mature than the Litvish 18-21 years old. And the Chasidim have a lower divorce rate despite getting married younger. Or, more likely, because of it. Once people gets older unmarried they each start getting into more meshugasim that they bring into marriage that a couple that married younger doesn’t have since they grew with each other together.
If one can do it, both can do it.