Guess I'm not experienced enough to know the nomenclature difference between a Pack Ride and a Pace Line. In this case one guy, about 20 years younger than me, got in front and told me we could practice drafting. I latched on and experimented with where best placement was and the aerodynamic effects. After a bit one of the other folks who had been riding behind me accelerated and took the lead. We sped up a bit. This repeated a couple times until we were just over 21. Still I was able to keep up without excessive strain. But, no way was I able to pull out, overcome the aerodynamics and advance to the lead.
I'd read about Pace Lines and thought this was just a variation. Whatever it was I learned quite a bit.