Born in late 70's here, and I've been using Google Wallet like this as well. I used PayPal for things like eBay back in the day before it became such a cluster, and I still occasionally use it when some ticketing system requires it.
But for the past several years I've just defaulted to Wallet ever since they added the ability to attach money to an email like you're attaching a file. I know it's just UI but that was sort of brilliant (if done in the typical fuss-less Google fashion so most don't even notice it).
So while I still lean toward buying rounds or taking turns paying for things with friends I see often, occasionally I'll be out someplace and unexpectedly need cash without a nearby ATM. If a friend has cash, I can just send them funds to pay back. Same goes the other way around.
Other times it's something like ordering tickets to an event and I just buy for myself and a few friends at the same time. Then if they end up going, they can forward me funds at their leisure and no messing with ATMs or writing checks.
Sounds like Venmo is used in a similar way but I've not started using it if only because I already have something I'm satisfied with and the handful of people who even want to use such a thing have it as well. I tend not to proselytize to other people who don't express an interest in doing things this way, but I've yet to run into anyone who is using Venmo.
Although maybe half a year ago I was single for the first time in years and saw a lot of people mostly-jokingly (I hope) on Tinder asking people to Venmo them $5 to get their attention. Seemed like either a cynical/ironic "why not?" sort of joke or the least ambitious prostitutes in history.