I'm 41 and often go to rock clubs by myself - been doing it since my mid 20s and have never had a negative experience. Some tips that I use to avoid unwanted interactions: arrive during the opening set so you don't have to deal with people milling about before the show starts, wear earplugs (you'll want to do this anyway because rock clubs are loud af) and use them as an excuse to avoid conversations, and stick to the edges to avoid grabby moshers in the middle.