The tl;dr is plant based protein is not the same as animal based. As we get older sarcopenia starts to set in and we need more protein. On top of that you need to be careful with what fruits and vegetables you eat if going 100% that way. Low vs fast starches and how it affects your blood sugar. The fiber in a lot of fruits and vegetables blunts the inslulin response but not all.
The more muscle mass you have the more you can buffer glucose spikes from creating free radicals. It is why peeps who exercise tend to live longer and look better whether its flushing excess glucose or having enough muscle mass to buffer it better. The whole longevity scene seems to be about controlling your glucose levels (which if prolonged causes diabetes, more arterial plaque for heart attacks, dementia (diabetes of the brain). Sugar in excess amounts causes inflammation which clogs up your immune system and then cancer comes in.
I can't really pin point to one video. I've listened/studied dozens of hours of this stuff. If you want to start studying look up Dr Rhonda Patrick, Peter Attia, Andrew Huberman, and David Sinclaire. Look at what the longest people living and what they consumed (they called it blue zones). It isn't exclusively meat or being vegan. Usually its a mix of both. There may be many paths but all have the same underlying principles like weight lifting.
Just from seeing pure vegans online they don't age better in fact worse. They also tend to get diabetes or heart disease likely from all the carbohydrates of fruit/vegetables they consumed.
Tl;dr im not a fruit/vegetable hater or a keto tard. I think all foods have benefits when used correctly and at the right time. A lot of fruit and vegetables have antioxidants like blueberries or Sulforaphane in broccoli sproutes. Lots of fruits and vegetables help with your microbiome too especially fermented stuff like Kombucha/Kimichi and more.