For what it matters...
I personally think it's just an interesting criteria, among many other possible ones.
I definitely don't see it as if it were "the be-all and end-all".
Nonetheless, it's still pretty impressive that Tadej at
26 years and nine months is
#9 according to the PCS
all-time rankings.
With all the guys left ahead of him who competed 35 or more years ago... aside from Valverde who is a very special case given that somehow he managed to be competitive till he was 48 y.o,
The ProCyclingStats alltime ranking is led by Eddy Merckx with 3859.8 points, before Sean Kelly (2171.1 points) and Francesco Moser (2129.2 points). Considering the enormous gap between Merckx and Kelly (3859.8) we can conclude that Merckx is the best rider of all time.
www.procyclingstats.com
Actually, I personally know that Valverde always lied about his age: in reality he was 57 when he won the WC in Innsbruck.
His last year competing in road races, when he won CG plus a stage at Gran Camino, did 2nd at Strade Bianche, 6° at Lombardia, and so on, Valverde was 64 years old.