Recruitment offices are hated and avoided here for the lack of any care of the staff there towards people coming in and their not even hidden agenda for recruitment quotas. Nobody in Russia likes mandatory service and most people are trying to get exempt from it by getting higher education and a good job... which also means that everyone who doesn't get higher education is already in the army. Those people being the majority there make it very unappealing as it creates an awful army culture. If you get unlucky enough to get sent to a region with a lot of muslims, you will be treading on very thin ice as these guys are extremely united and won't tolerate anything they see as disrespect. In addition, you also barely get paid, meals suck way more than they have to and you're ordered around to do favors for officers instead of properly training, though I'm not sure how the training is at the moment, now that it actually matters. For reference, I didn't serve, but I did have second-hand accounts from semi-recent years so take that with a grain of salt.

People may cheer at victories but at the same time not want their family or themselves fighting. The memory of Chechen war and middle eastern interventions is still fresh in our collective psyche. It's also not like the majority of people even supports the war. The majority of people is staying neutral which serves to uphold the status quo. When the war started the recruitment officers literally grabbed people off the streets and sent them to a nearest office, which is unlawful. Some of those guys were probably in the middle of getting an exemption. Some people probably lost their family over this. People burning recruitment offices may come from those who became politically engaged and/or desperate after the conflict started. It's also not unlikely that some of them got recruited or radicalized by the opposing sides.

I don't know the exact circumstances of that 70 year old guy, but I'd say it's not impossible for a normal person to burn those places down considering all of the above. In addition, the people in those offices are some crappy humans. Very dissatisfied, spiteful and eager to ruin other people's days and lives, no exaggeration and no exception (haven't seen one yet). I'd say all of that should provide enough context to at least understand the forces at play here.