Progressive decline or huge drop?

I've always been curious to observe and measure my own decline as I get old enough to witness it and feel it. So far, my observations have been quite rewarding and for the past 4 years, I've observed that I get tired quicker and need more sleep than in the past.

The end of this winter has been quite hard on me though; even though I skied a lot and still well enough (I think) my legs feel stiff like they never have before. Instead of being a progressive decline it feels more like a huge, sudden drop.

I tend to put that on the account of the spring season that, as I always heard, plays havoc on many people and beats them up.

I hope this is true, but, on the other hand, the spring of my life can't last forever either!