Around 40 ni Natta Saikyou no Eiyuu-tachi, Futatabi Senjou de Musou suru!!

The century-long war with demons was finally brought to a close by seven young heroes who slew the demon lord, routed the demon army, and ultimately led humanity to victory. The heroes then went their separate ways, and the land has been at peace for twenty-five long years...until now. Alan Granger, a former hero, enjoys a quiet life as a commander in the Royal Knights until the day he receives a report that shakes him to his core: the demon army has returned! He immediately knows what he must do—gather his old compatriots and face the demon army once again. But Alan and his friends are now all in their forties, while the demons are more powerful than ever. Do these veteran heroes have what it takes to leap back onto the battlefield and save the world a second time? (Source: J-Novel Club)