Being vegan in 2023 is extremely easy, but to me that seems like a relatively new phenomena.
So if I put you in my vicious time machine and sent you until the dim past, how far back would you be vegan?
I think I could make it work for most of the 1900s. But if I was in 1500 I'd give it up.
Veganism means avoiding animal exploitation where possible and practical, so theoretically you could be vegan in any time period as long as you never ate more than the absolute minimum meat you needed to survive.
My mind went to other animal products like furs, leather, bones, and animal transport. Depends on where you live, I guess.