De Niro was evidently 5' 9 1/2" in his prime, which is just about spot-on average for a male in the U.S. He turns 81 in two weeks, so I imagine time has compressed him by an inch or so. However, from what I can tell, the ridiculous-looking platform shoes were taken out of context. He wore those in the 2019 movie The Irishman because he played a character who was 6'4". Photos from that, and from his Tonight Show appearance wearing them when he was shilling the movie, are easy to find on the web. Just DuckDuckGo "robert de niro platform shoes".
I'm most definitely not a fan of De Niro's politics. But the YouTuber is purposely misleading us with this little clip.