LARPing is geeky. No way around that. I'm a geek myself and have tried it a few times, never enjoyed it quite enough to invest in any kit though.
Re. Meeting girls: Most LARP groups I've been part of are at least 25% girls, more often 35%+ It's not just for blokes. Girls really love the dressing up, acting as a character and so on.
Re. Developing himself: LARPing relies heavily on making decisions as a group under time pressures, with strong negative consequences for making poor decisions. This is incredibly valuable training for real life, certainly more useful than any number of other hobbies e.g. drinking, watching TV. You get huge amounts of practice weighing up pros and cons, being decisive, and working with others to achieve a goal.
Re. Physical health: He's running around outdoors, and actually fighting with people using swords. It's pretty damn healthy.
Re. Life skills: It can actually stimulate an interest in all kinds of practical things. Cooking on an open fire has been mentioned, but there's also sewing, repairing damaged equipment, creating new things, repurposing everyday objects to serve as props, and so on. It also encourages acting as a skill, and serves as an endless font of creativity.
Despite the rep as being incredibly sad, it's about as productive and useful a hobby as you're ever going to find.