When I started 42/52 & 12-21 was the norm, which I used until I was about 50. I always climbed seated in fact did my whole ride seated (with the exception of Chimney bank and some climbs in Wales like Bwalch y Groes.
I did my first 500 Carlton banks seated using 42/19, and used to do Chimney on 42x21...which is very difficult!
How things change with age, in just a few years since then I have gone to 42x25. 39x23 then 25. Compact 34x25, tried a triple, 30.42.52. I found all these worked with my original C.Record mechs.
I started standing on the climbs due to back and hip problems when about 52, and now have settled on triple 30.40.52 with 12/26 at the back and always stand climbing, I avoid the really steep stuff unless its dry as you loose traction standing.
I blame the decline on Strava as you can not race up hills with such difficult gearing or seated although age must play a part.
But... as with most things everybody is different.