The Middle-aged Deliveryman Becomes an Invincible Swordsman as a Side Job is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Jack is a boring middle-aged deliveryman leading an ordinary and uneventful life, until one day, he’s suddenly called to the royal capital. Having no idea what he’s done or what’s in store for him, Jack heads to the capital, but waiting for him there was…?!