He looks amazing for 30! If I were the judge in the halter class, he'd get first just for showing up & longevity. He could use some more weight, and needs it on his top line which is where it's hardest to get. You don't say where you are, so I'll go by what I'd feed here because it's easy to get. Purina Ultium & Alfalfa pellets. You could also get Ukele's Tri Amino summplement, the amino acids are great for putting weight up at the top line. And of course, lots of hand walking and up/down transitions to muscle him up a bit.
But seriously, he looks great for his age! You're obviously taking really good care of him.