I'm 20 and I've never heard of Venmo outside of HN. To be fair, I am also in Australia, so it's more likely that it just hasn't caught on. The major bank here (CommBank) has made paying other people frictionless (you can send money to a phone number, via NFC, cardless cash, or just by regular transfer) so it's likely that Venmo wouldn't have much of a market here.