I've gone through this at a similar age with several of my previous dogs. I think they often do go through a fussy phase. All mine gre out of it eventually.
There seem to be two schools of thought on how tomapproach it. The first is to just leave his food down for 15mins and then remove it. Put it down again a bit later and try for another 15 mins. The theory being that they will eat when they are hungry and learn that if they don't eat, the food goes!
Personally I prefer my dogs to want to eat and enjoy their food. Archie became incredibly fussy at about 6 months and stopped eating altogether. He was on kibble mixed with nature diet. He started off just leaving the kibble but then refused to eat anything. I tried various different foods but eventually ended up just feeding him wet food with no kibble (Wainwrights trays, which he adores). Once I found the food he likes we never looked back.
I think it is up to you whether you just persevere and hope he starts eating again once he knows nothing yummier is coming along, or if you try to find something that makes him enthusiastic again. I know a lot of people feel that by doing this you run the risk or creating a fusspot, always on the look out for something nicer.
As a first step, I might try him on just kibble or just wet food - perhaps it is the mix he doesn't like? Also try leaving him alone to eat as it is possible that he is picking up on your worry about him not eating.
