The year in which the story is taking place now is 1910(3 years before Muzan killed Kamado family)
The age or status of the characters are
Satoshi:14 years old
Rengoku Kyojuro:15 years old
Tanjiro: 10 years old
Nezuko: 9 years old
Mitsuri: 14 years old (Not joined demon slayer corps)
Obanai: 16 years old (saved by Shinjuro Rengoku)
Giyu:16 (Hashira)
Kanae: 16 years old (Hashira)
Shinobu: 13 years old (in demon slayer corps)
Gyomei:22 years old (Hashira)
Water Hashira:
Flame Hashira:Rengoku Kyojuro
Sound Hashira: Tengen Uzui
Water Hashira:Giyu Tomioka
Stone Hashira:Gyomei
Flower Hashira:Kanae