who is the oldest hashira

The title of the oldest Hashira in the anime 'Demon Slayer' goes to Gyomei Himejima. His age isn't officially disclosed, but he certainly carries the demeanor and wisdom you would associate with being the oldest. He's the Stone Hashira, one of the most powerful fighters in the Demon Slayer Corps, renowned for his immense strength and spiritual concentration. Despite his physical prowess, Himejima's approach to life and combat is marked by deep humility and fervent piety. He is kind-hearted, often seen crying for others, which IMHO is pretty wholesome.

Himejima is visually distinctive with his large stature, shaved head, and blind eyes - Fun fact, he’s one of the few blind characters in anime who doesn’t let his lack of sight limit his combat skills. Quite the opposite, he's developed his other senses to superhuman levels, making him a formidable adversary against demons. His weapon of choice is a unique one - a spiked ball and a hand ax tied to a long chain, which perfectly complements his brute strength.

One other thing that I like about Himejima is that, despite being a man of few words, he's a figure constituting moral strength and compassion. And his backstory is oh-so-heartbreaking; it adds a depth of character that makes him all the more interesting.
         
So yeah, next time when you're lost in the captivating world of 'Demon Slayer', pay a little more attention to Himejima – there's much more to the Stone Hashira than meets the eye. ( or doesn't, if we consider his blindness) - His character embodies resilience, courage, and kindness, a perfect example of the older, wiser, and stronger trope, delivered with excellent subtlety.