Actually, that age scale is an old wive's tale. Depending on the size of the mature dog, the comparable growth in the first year can be between 12 and 18 of our years, followed by a rapid relational slow down until (again, depending on size, but also general health and diet) after about 10 to 12 they age at about 1.5 to 2 years per one of ours. Still, at 14, your dog is most definitely a senior.
On a general scale, cats are pure carnivores (they eat grass to make themselves vomit,) dogs are mostly carnivorous omnivores, while we and bears are omnivores, and cows and deer are herbivores. (BTW, only the herbivores digest corn well.) Dogs generally eat meat even into their old age as THE main ingredient in their diet. On their own in the wild, dogs will eat meat up until they can no longer hunt and can't find carrion to scavenge (basically, until they die.) However, if you haven't been giving your dog meat (preferably raw,) you should introduce it very slowly, a little at a time over a week or two to let his system adjust.
If you don't want to feed deep water salmon, look for a premium dry food that contains at least 0.03% DHA (or Docosahexaenoic Acid.) I know Nutro Ultra Senior does but most premium foods that include salmon meal in the first 10 ingredients probably do as well.
Oh, and you may want to look for taurine on the label as well. It's mandatory in cat food, but still optional in dog food. It helps the eyes and the heart so it may help with his light sensitivity.
Just don't buy any of the 'junk' foods that state 'DHA' in big letters on the front but are full of by-products, lots of regular cornmeal, sorghum, peanut hulls, etc. Ugh!