50 years old. WOW!! Harrison's is often suggested by vets, but many birds won't touch it. I'd suggest Zupreem Natural large parrot. At his age you should stay low on sugars & artificial colors. It won't be easy getting him to eat pellets. You should cut back on the seed mix slowly, but you also don't want to stop seed mix totally. Some seed mix in his diet is OK. I'd start by giving him pellets in the morning, along with a little seed mix, & other regular foods at night. Remove all food from his cage before you go to bed. That way he'll be hungry in the morning when you give him the pellets. You can also offer the pellets wet & see if he likes them better that way. Also offer veggies like cooked sweet potatoes & carrots, peas, corn, any greens, etc., or what ever you can get him to eat & some occasional fruit, again late day/evening. Offer veggies that are higher in Vitamin A. Use only fresh or frozen veggies, never canned. This will take time & once you get him eating them you can change up what foods you fed at what time of the day. I'm trying to get my soon to be 21 year old B&G Macaw to eat less nuts & more pellets. She seems to prefer eating more pellets in the morning hours than the rest of the day.