There’s no way he’s younger than 50, and that’s if he was just 10 when the Rocks shit went down. Not entirely outside the realm of possibility - Buggy and Shanks were children on Roger’s ship, Koala hung with the Sun Pirates as a kid, and Jack was fucking eight years old during (and still implied to be involved in) Oden’s execution - but his silhouette from the Rocks reveal made it look like he was at least in his 20s, assuming Linlin/Newgate were in their 30s then.
I’ll say he’s in his mid 60s now, unless it’s revealed that he’s actually an oni/other sort of creature that took on a humanoid form, then he could be decades or even centuries older than he looks.