This year the Slip-N-Slide is 52
The Wham-o Toy Company introduced the Slip-N-slide in 1961 after being invented by Robert Carrier. The long sheet of plastic became a huge hit with kids and has been a main stay of summer fun for years. The best part was all you need to make it work is an ordinary garden hose.
Since the toy was introduced there have been various enhancements like an inflatable pool at the end and spray tubes on the sides.
I would say the biggest development has been how the adults have taken it to the next level. That has produced a ton of great footage of people having big fails on them.