Valverde defies the current trend of older riders retiring then un-retiring. Like Alberto Contador (riding for Trek-Segafredo in 2017 after saying he would quit at the end of the 2016 season), Joaquim Rodriguez (now riding on for one more year with Bahrain-Merida) and Giorgia Bronzini (persuaded to stay on at Wiggle High5 for another year by Rochelle Gilmore).
He just keeps on riding. When he'll stop is anyone's guess. Why not 40, 41, 42..?
Considering his prolific output, over the next three years he'll surely add to his four WorldTour individual titles, one Vuelta a España GC win, podium finishes in both the Giro d'Italia and the Tour de France, three wins at Liège-Bastogne-Liège, four at Flèche Wallonne, two Clásicas de San Sebastián, two Critériums du Dauphiné and four Vueltas a Andalucía.
There's not much left to say about a rider who is the most complete of his generation, except to sit back and enjoy his aggressive and dynamic racing style for the next three years.
(*yes, he was pinged for doping and served a suspension (2010-2012), but so was everyone else at that time. Just let it go.)