I have now been sailing for 36 years.
The first picture is from 1989, I had already been sailing for 11 years. I had been Guernsey Wave sailing champion and Slalom champion. Speed hadn't come into the picture yet. The second form 2013, same bay, same wave.
The third picture is from 1994 ish in St Marie de la Mer, my fourth year of speed and already an equal 4th place finish in the 1992 overall standings. The fourth is from Luderitz 2014, by this time I have had a second place in the 2010 overall standings and sailed over 50 knots.
I might be blowing my own trumpet here but I think I'm getting better at windsurfing !!
Bjorn recently stated that to be competitive in PWA wave sailing 35 is the maximum age. I would agree with that, you don't see many over 35 year olds double looping.
Bjorn has just retired from Slalom at the age of 46, that has got to be the limit.
What about speed? In the overall 5 x 10 sec GPS standings 9 out of the top 15 are over 40, most closer to 50 or above. Personally I think you can be competitive at speed records up until 55. Speed contest I think you are going to struggle past 50.
All good news for us oldies!