I suppose it's very different depending on where you live. I live in a small-ish city and most players I encounter are adults, and the most hardcore players are definitely adults. (It's hard to be a power raider without independence, money, and a vehicle, which not too many kids have. ;D ) I do see the occasional group of teenagers playing on foot/bike and the younger kids I see are usually being hauled around by their vastly more interested parents.
I usually do the "I see you are also playing PoGo" smile/phone wave/nod-of-acknowledgement and keep doing my own thing, unless I'm at a raid and no one else is doing the organizing.
Although I do look young and was quite recently angrily yelled at by some guy about how "adults don't waste their time doing stupid shit like pokemon" and laughed to myself about how wrong he was. So I can understand the desire to keep your playing a secret.
There's plenty of pros to socializing, although there are also definitely.... cons. Best medium is to get a small group of good friends together and play with them, imo.