Found it by chance (Sono Rettou Kishi, Level 999)

[Nyanyan444]

I'm looking for a manga about this strong mc but his parents told him his not strong enough. What i remember is his parents like a warrior who fight demon lord when they win the god give them of youth spell so they can make their own child. When the mc is 14 or 17 he want to became a knight and begins his journey and this girl (I don't really remember about).

My explanation is so messed up but hope you know what I mean.

 

[Nyanyan444]

It's not isekai and actually the demon lord is looking for him per his parents request (the demon lord not joint his adventure it just once in a while he looked the mc and ask how his doing)