Boukensha License o Hakudatsu Sareta Ossan Dakedo, Manamusume ga Dekita no de Nonbiri Jinsei

I'm a Middle-Aged Man Who Got My Adventurer License Revoked summary:

Douglas, once known in legend as the strongest magician.

But now he is called old man, as his health slowly crumbles. Beyond just suffering from a mysterious disease that slowly, but permanently, saps his health if he uses magic, the hero's party forces him out and the adventurer's guild strips him of membership.

Thus, in the middle of an aimless solitary journey, the ex-adventurer Douglas encounters a cursed girl, Ravi.