Do you perhaps mixing two works with similar premise? I'm certain I'm familiar with both of them.
There's [100.000 years of Qi refining] which is set in normal xianxia universe, and the baby-faced MC have actual old man mentality for being so old and tired of not ascending after 100.000 years of cultivation.
There's [10.000 layers of Qi refining] which is set in pseudo-modern world, and the MC is just typical cold asshole and he thought that if he can reach the 10.000th layer he might be able to break through. He's still old, but more like, hundreds of years old and act like he's 30.
Since you're talking about manhua, it might be the second one, which is awful to read and very, very sexist. However, how you characterize the MC sounds like the first one.