Hi Ian,
This is a gorgeous little portrait. There is good detail in the face and we can tell from his expression that he is enjoying the day. If I was a member of this gentleman's family, I think I will be rather happy with this photograph.
On the whole there is not a lot that I would do to adjust the image, but here are two small considerations.
Where possible I would rather not have a vignette fade off to black in the edges. That green in the upper right of the image is beautiful and I would love to see that gently fade off to the corners without going black. That would improve the image so much.
My only other concern is the brightness on this gentleman's eyelash in the left of the picture – it is just a bit too bright. Given the chance I would gently pull it back with a gentle touch of the clone tool (with the flow is set to about 5%), or with the burn tool (with the range set to highlights).
But that's just me being fussy!
Cheers,
Anthony