This meetup in particular currently has 6 RSVPs under 40, 2 under 50, and 2 above. You are actually in the average...a bit young is under 22. Hope that doesn't make you feel older.
Speaking from my own experience having been in BA since 2013 and hosting these meetups in both BA Expats and in Meetup.com, I've made many friends in the broadest of age ranges, from the widest variety of countries, from the broadest of cultural backgrounds, and with a variety of professions. I've made many more good friends during my time in Buenos Aires than I've made in the 10 years prior to that.
I hope you don't age yourself out of meeting some cool people, and we get to meet in person. In any case, if you want to come by and scope out the group prior to committing to walking in and grabbing a seat at the table, Padre CR&B has two walls that are completely windows so you'll have no trouble seeing us.
I'll be the one in the GUAM baseball cap sitting with all the younger people (kidding, I'm quite young myself ).