Adjective for 'old' which can be used for age?

Dictionaries invariably note that you cannot use ふるい for age of a person. So what adjective can you use? Ive been forced into awkward circumlocutions which I'm sure are wrong; what is the best word to use for 'old' as applied to a person? There are nouns for a 'senior' etc such os せんぱい and of course the counter for years さい but none of them easily or directly translate 'old' as used in English regarding a person.

I think you can use "rounen" to mean "old age", and use it as a ~no adjective. So like, "rounen no otoko" = "old man."