As someone who has just started this journey I'll add my 2 cents.
It was my son who suggested we try airsoft. He's only 12 but having played with Nerf guns (myself aswell) for a few years he wanted to try airsoft.
After he got over the initial shock of being hit he really enjoyed playing. Personally I enjoyed it more than I thought I would!
Cost - I think its comparable to other hobbies, fishing, paddle boarding, and cheaper than many, cycling, golf, sailing.
Heath - I don't think this is mentioned enough, outdoors (mostly) and as physical as you want it to be, I know I come home knackered...
Social - Team building, meeting new people, sharing experiences
Mental - Keeping your brain active with marksmanship, strategy, problem solving.
Most of all its fun and a good way to forget your day to day troubles.
I'm not playing airsoft with my son to train him to be a killer, we are spending time together, he's getting more confident and learning to be responsible. I think its a great outdoor activity and good value for money.
You can tell i work in Marketing LOL....