Reply To: Any heter to not get drunk on Purim?

What do you mean? This isn’t a matter of chumra or kula; it is a matter of psak halacha. If a posek holds it is a chiyuv to get drunk k’peshuto on Purim, which is a clearly a valid shitta that is held halacha l’maaisa by various poskim, then that’s the psak halacha for anyone who has him as their mora d’asra or posek.

Dina d’malchusa doesn’t override halacha, as you’ve acknowledged above. And halacha doesn’t distinguish on this between a 13 year old and a 22 year old.

The only distinction I see if the person cannot handle the alcohol and it is a sakana to him. But that would be an individual heter to deviate from the halacha, which is something that is sometimes muttar. But if someone under 21 is as physically capable of handling the alchol as a normal person aged 31, there isn’t a halachic difference between the two of them on Purim just because one is aged 20 and the other is aged 22, irregardless of the secular age 21 arbitrary cutoff.