In the tour de france the average age was over 30. In the last 15 years that never happened.
The average ages of the last 15 years. Without exception the Tour de France was the oldest each year
The rider age was calculated in days and not in rounded years. The first day of the grand tour was used to calculate the age.
The Tour de France riders are on average 8 months older than Vuelta and Giro riders. The average age of the Giro and Vuelta are not so different. But remember that the Vuelta starts 4 months later than the Giro. That is an extra 0.33 years
Surprisingly the average age of riders who finish the grand tours (28.74) is about the same as the starters: 28.72