Weed, sure.
Prostitution? Fuck no. In fact men seeking the services of prostitutes will be punished even more harshly than now. Millennials will also make sex dolls and all forms of pornography (including hentai) illegal and a felony to possess. If you think that sounds far-fetched, consider the fact that pornography is already illegal in much of the world, full stop. Not just for religious reasons either, because China and South Korea are both fairly secular and it's banned there. There have been Korean hentai artists and doujin translators that have gotten harsh prison sentences.
Also consider the fact that in the west, the most affluent and politically active millennials are SJWs and numales.
Your future law makers, judges, and leaders:
Still looking forward to the boomers dying?