That's what I thought too, he looks like in his 60's and not in 40's usually in manga when it comes to old man they make it their eyes looks old by drawing some line and when it comes to 60's they add some lines near the mouth.
usually especially people in asia have like crazy genes and age super well...the master at the temple i am at here in my country is also chinese and dude is also almost 60 already but looks like 40 or something....sure it does not apply to everyone...but generally yes....especially 40 is often the age where some men look their sexiest haha...around 30-50 some can look freaking fine being finally mature and calm and shit....
So, the old man is 40 years old, and they are making him look like he's 60.
People who are forty don't look that old, unless life was extremely harsh on them.