Tanjiro's strength in the manga is significant. He acquires new powers and techniques, and overcomes numerous powerful foes with determination and strategy.
Well, Tanjiro's fate in the manga is tied to his determination to save others and the ultimate confrontation with powerful foes. His death comes as a poignant end to his heroic journey.
Tanjiro is believed to be 18 by the manga's end. This age is a result of the events and time that has passed since the beginning of the story, showing his maturation and development.