We have a new kid to join the select club of Grand Tour winners who are still active, the 8th. I considered the breakthrough for all, the first top 10 achieved.
First the younger one:
Simon Yates, breakthrough at 24 in 2016, 6th Vuelta, first GT win at 26 in Vuelta 2018
Then the 1990 generation:
Dumoulin breakthrough at 24 in 2015, 6th Vuelta, first GT win at 26 in Giro 2017
Quintana breakthrough at 23 in 2013 second in Le Tour, first GT win at 24 in Giro 2014
Aru breakthough at 23 in 2014 third in the Giro, first GT win Vuelta at 25 in 2015
The older generation:
Froome breathrough at 26 in 2011 second in Vuelta, first GT win at 28 in Le Tour 2013
Nibali breakthough at 24 in 2009 6th in Le Tour, first GT win at 25 in Vuelta 2010
Valverde breathrough at 23, third in Vuelta 2003, first GT win at 29 in Vuelta 2009
Thomas breathrough at 32 first win at 32, Le Tour 2018
First the younger one:
Simon Yates, breakthrough at 24 in 2016, 6th Vuelta, first GT win at 26 in Vuelta 2018
Then the 1990 generation:
Dumoulin breakthrough at 24 in 2015, 6th Vuelta, first GT win at 26 in Giro 2017
Quintana breakthrough at 23 in 2013 second in Le Tour, first GT win at 24 in Giro 2014
Aru breakthough at 23 in 2014 third in the Giro, first GT win Vuelta at 25 in 2015
The older generation:
Froome breathrough at 26 in 2011 second in Vuelta, first GT win at 28 in Le Tour 2013
Nibali breakthough at 24 in 2009 6th in Le Tour, first GT win at 25 in Vuelta 2010
Valverde breathrough at 23, third in Vuelta 2003, first GT win at 29 in Vuelta 2009
Thomas breathrough at 32 first win at 32, Le Tour 2018