I think I'm healthier than most people. More healthy in my 30s than my 20s - throughout most of my 20s I still ate animal products, took antibiotics, drank diet sodas, and all of that mainstream garbage. Through becoming vegan I seem resistant to upper respiratory infections and coughs I frequently see in my class mates - there are people who have been hella sick 2 or 3 times just the semester, but nope not me. I tell them to stop eating dairy, and they're like "I do when I am congested" and I'm just like "uh no - stop eating dairy. Like at all. Once you're sick it's almost too late."
I do get the flu maybe once every year or two, but I've talked to medical professionals about this, and they say even getting a flu shot leaves you with a 50/50 chance of still getting the flu so why bother.
I had health concerns about veganism in my early 20s, the first time I tried to do it, and really lacked information. Vegan diets are complete you can get all of your amino acids, vitamin K, whatever you need - Omega 3s are in hemp, walnuts, canola and flax, and K2 is produced in the gut of people who eat fermented foods like sourkraut, pickles, kombucha, etc. not by animal flesh. The only thing you should absolutely have to supplement is B12 which you can get in fortified milks and nutritional yeasts, or receive as a shot, if you don't like taking vitamin pills. Even as a vegan you only need to take a B12 once or twice a week, you don't even have to take it every day.
Eat a variety of foods and don't rely on junk food as your only sustenance. I'm weirded out by vegans who try to live off of Oreos, french fries, and vegan pizza - I'm like you can't be serious, right, this wouldn't even be healthy if you weren't vegan.