Hi there. It sounds as if he may have a respiratory infection, which he may have succumbed too because his immune system is not as strong as it once was (due to age).
It would be a good idea for him to have a course of antibiotics, in case this is a bacterial infection.
You can get an antibiotic called 'Terramycin' very often without prescription, if you're unable to get to a vet, it contains the drug 'oxytetracycline' which is good for respiratory disorders.
The dosage is 4-12mg/litre of water for 7 days.
Alternatively you can get other antibiotics on prescription from the vet which may be much better, such as 'Baytril' and 'Doxycycline'.
This may help
Regards Andrea
Bird Veterinarian
15 years in companion animal practise, BVM&S degree Edinburgh university