It's more like an interactive zombie movie. Infected and players are not the same. Infected are never friendly, they're down right dangerous, you'll want to avoid them, certainly at first. Players you meet may or may not be friendly, or act friendly then stab you in the back and steel your stuff (gosh, it's almost like the real world).See. Second verse. Same as the first.
You basically start in your underwear, hungry and cold. First order of business is finding food and something to drink, avoid all infected and other players. Plenty of times I died of starvation before getting some marginally good gear. The map is huge (25km2), no vehicles (there are some now, but not when the game was first released), resources are scarce, firearms definitely are. You may find a hunting rifle in some farm house but no ammo. Ammo is scarce too. So you often can't even use it. There is some better stuff in various police stations or army bases, but those attract other players too. For the same reason you are there. And honestly you don't want to use a firearm, sound travels far. It'll attract more infected and other players will be aware of your location too. It's much more like a cat and mouse game, with you being the mouse, trying to hide as much as possible. I've had great fun playing this with my buddy. There have been many times where I thought I'd die laughing in real life because of some stupid situation we got ourselves into.
That said, I can understand this type of game (or any other shooters) might not be your forte. But there are plenty of other genres, role-playing game perhaps (think D&D)? Turn-based strategy? Management games (football manager, baseball manager, etc)? Not all movies are the same either, with different genres catering to different groups of people. I like certain movie genres more than others. Same with games. And it's been half mentioned before, they can actually be beneficial for older people (yeah, including you old fart!). They keep your brain flexible, cognition improves, coordination, a lot of good things.