Yes, it is highly recommended for older people to include fish in their daily diet because of the following good reasons:
1) High in Omega 3 fats:- Fish is a very good source of omega fatty acids that helps your body to resist winter infections and absorb more fats and carbohydrates to keep you warm.
2) Prevents from age related disorders:- Diseases like dementia and prostrate cancer are staved off by eating fish
3) Wards off depression:- Fish has richness of essential oils that cures depression in older people.
If you wish to know about organic fish, then read here.