when u turn 50, you get a day off for your birthday. so definitely your mgr and teammates know your age if you're 50+
I've never heard of a birthday off for turning 50.
However, Cisco did start granting a day off for your birthday that didn't count against your PTO balance for all employees. It started sometime shortly after CR took over as CEO. You're supposed to use it within 1-2 weeks of your birthday with your manager's approval.
I'm one of those nosy people on my team that knows everyone's birthday. I may or may not know the year, but I put the date in my contacts for that person whenever I hear them talk about their birthday or someone wishes them a happy birthday. Then I make an effort to wish them a happy birthday every year there after, even after I switch teams.