Mannen D-Rank no Chuunen Boukensha, Yotta Ikioi de Densetsu no Ken wo Hikkonuku

Lucas has a hard life. In his mid-thirties, a mixture of failures has left him old and crippled, playing pack mule to a couple of young adventures. Then one day, he pulls a magic sword from a stone that tells him he has been chosen to become a hero. Given a youthful form, Lucas must use the power of the sword to vanquish evil and attain a massive harem.

(Source: MangaDex)