Medicine can slow down your decline man, but you would still decline. Testosterone levels start to decline from late 20s itself, even in this modern world players do decline in their 30s but the decline is slow.
See always remember, whatever "medicines" an old guy is on, even the young guy is on that, so if both you and old takes the same stuff then young always wins because of biology. Sports like Tennis is not like Cricket or something else where we can be in your prime in 30s, it doesn't work that way.
The Big 3 won so much after 2016 because the 1990s generation's best player is Medvedev who is a Roddick level player at best. If an entire generation lacks talent then the result is someone picks those slams meant for them, in this case BIg 3.... and since Novak is the youngest of the lot, he picks the most. If Federer was on Djokovic's age then Federer could have also picked more into the share of spoils, but here it is all Novak and a bit of Rafa,
Okay with Big 3 being better than the rest argument.
Not okay with the selective peak selections of players. You peak when you win and aren't in peak when you lose is very very selective.
To any rational viewer of the sport, all of big 3 played most of their matches while being in their peak. Esp when they reached the late stages of slam, they were def at their peak.