I have to agree with the last comment and wouldn't leave the food down as it will just encourage him to be fussy. There have been quite a lot of similar posts on this subject recently, a lot of them about dogs around that age, so I do think it could actually be an age thing. It is very hard but I would doubt very much that a dog would willingly starve himself, if he's hungry he will eat it, (especially if he knows there's no more, if he doesn't hurry up!
) Humphrey went through a similar phase, I gave him 15 minutes and what wasn't eaten was put down at the next meal or thrown away.
I made that mistake with my first dog, we had food standing around all day, I lost track of how much he'd eaten and how long the food had been there and he was a fussy eater all his life. I'd never do it again.
I would say persevere, I'm sure he'll get there!