Another thing that has changed is the rise of young riders, not just Seixas. Spencer Martin pointed out that over the past few decades of the Tour, the average age of the peloton has been 29, and so has the average age of the top ten finishers. In the past few years, the average age of the peloton has stayed at 29, but the top ten finishers average age has dropped to 25. If this is a trend, then bike racing could be going the way of women's gymnastics, where young athletes dominate and competitors in their late 20's are team fillers. Time will tell.
Used be 27 was the perfect age to win the tour because you needed that hard won experience while still not too old. Radios have changed all that. Though have to say some DSs instructions over the radio leave a lot to be desired! But in general now the experience of former pros in the cars can advise straight into young GC contenders ears making up for their own inexperience.
I would say the select few riders like Pog were born with a canny ability to match their physical gifts -at any age.