Botsuraku Yotei no Kizoku dakedo, Hima Datta kara Mahou wo Kiwametemita @comic

Liam Hamilton is not who you think. On the surface Liam is the son of a failing noble family, but on the inside...he's actually a lowly peasant?! One night he's a miserable middle-aged commoner chugging cold beers at the local tavern and the next day he suddenly wakes up as the youngest son of a noble count?! Make it make sense! Liam Hamilton has no idea how he ended up this way, but he does know one thing for certain: as a noble he can finally try learning magic like he's always dreamed of! Too bad the noble house he's been reborn into is on the verge of collapse–that is–unless they prove themselves worthy of high society. When Liam discovers he has a natural affinity for magic, can he save his doomed house or will he go back to being just another lowly commoner?

(Source: J-Novel Club)