Turned 50 last weekend, have been riding for 20 years, and racing age category level for 15 years. Most races are good, but occasionally things go pear-shaped; it happens.
The years have seen anywhere between 400-450 hours, or 20-24k TSS (if that means anything). That’s all I need to be semi-competitive in that category; ride at the pointy end of the bunch, and finish with the bunch. Get to ride the next week, instead of taking risks and ending up drinking my food through a straw or IV.
To get adaptations, I build, ride the peak, then let the fitness fall. Build again, peak again and let it drop again. Some years I would ride the plateaux just to keep things interesting. Note that build and peak is to let the fitness climb to an A-event, not the mesocycle referred to as build.
Some friends have asked how I can allow my fitness to drop so far, fearing it will be gone. It’s easy… let them beat me through the year and I’ll beat them when it counts.
I’ve polarised my training, done the whole sweet-spot thing, as well as block periodisation and usually end up with similar results.