In modern Japanese, 老い is a common word but it almost always refers to "aged state" or "aging process" rather than "aged person". You can say 老いを感じる, 老いを迎える, 老いに打ち勝つ, 老いの波 (figurative expression), etc. In this sense, I think jisho's definition is somewhat confusing.
But as an exception:
- There are a few rare compounds where 老い works like an adjective meaning old. 老い木, 老い松, ...
- There is a relatively common set expression 老いも若きも, where 老い seems to work as a noun meaning old people. As far as I can recall, this is the only case where 老い refers to people.
Outside of the set expression 老いも若きも, you should use お年寄り, 老人, 年配の方 or such to refer to old people.