Oh, so this is about any NES game? Well that's a completely different story. Anyways, saying only 1% of 16 year olds can beat an NES game is like saying only 1% of 36 year olds know how to send an e-mail.
All I'm saying is this. If you take a 16 year old who's only ever gamed on 360/PS3 to now, playing only modern games, they're not going to have the skill set that someone does who has gamed since the NES because modern (not retro indie platformers etc.) games are soft in comparison.
Can someone who is young be raised today on hard games and have those skills? Sure, and there's many out there that do... but it's not the majority or even close.
There's probably a rather simple explanation for that: If you've been gaming ever since the NES era (not the same as simply having gamed in the NES era, then quit gaming) then you are what is often reffered to as a "core" gamer, where gaming has become an important hobby for you. That would also mean that you've spent a lot more time gaming.
To further explain, my dad used to game back when he was a kid, but he doesn't game anymore, and he'd struggle if I were to give him a game of moderate difficulty today (not to mention any hard retro style platformer). Likewise, a lot of people that have only gamed since the PS360 era are likely to not end up as so called "core" gamers when they grow up, however given that they (us) aren't as far into our lives, the, ahem, let's say, wheat hasn't been separated from the chaff. While for people who have been gaming ever since the NES era they have, and you are left with the so called "core" gamers.
Of course yes, games are easier today and that will lead to a skill difference for the average gamer, but I don't think it's nearly as big as you make it out to be.
IF you were to just pick a random dude who used to play on an NES, and ask him to finish Contra, he'd likely get his ass whopped, same can be said for a random kid who plays on his PS360 or PS4/XBO.