2016 is PS4's 4th year.
It's the PS4's 3rd full year. Technically 2019 is the Switch's 2nd full year... but whatever it's the best we can do. xD
Predictions (Made July 2019)
LTD: PS4 - 130m, Switch - 110m, XBO - 52m 2019 : PS4 - 15m, Switch - 18.8m, XBO - 4.8m 2020: Switch - 22m (Peak Year)