Dog not eating a lot

I noticed my 8 yr old dog has not been eating a lot.. He puts his nose up at his food. I tried different methods.. Warming it up in a different bowl .. He ate it then.. Out of my hand  he ate it then as well, he seems to be drinking a little more than usual as well.. He has a cold nose and is waging his tail .. Barking good etc.. He is also going to the washroom . Could he just be picky or could there be done teeth issues .. I think I may be just paranoid ..