Is it correct to say "aging X years or more"?

Hundred participants (aging 18 years or more) were selected from each of the cities.

Is the phrase within the parentheses correct? Any suggestion to better express the idea will also be appreciated.

Ditto Cornbread.

"Aging" refers to either (a) as a verb or gerund, the process, or (b) as an adjective, the state of being old.

An example of (a) would be the common idiom, "Sally is aging very gracefully", meaning that while she is no longer young, she looks good for her age. Or more pragmatically, "Aging often comes with many medical problems."

An example of (b) would be, "Our nursing home provides a variety of services to aging individuals." It's generally consider something of a euphemism for "old" -- you're not old yet, you're just aging.

They are already there, so you'd want to call them aged. Additionally, I would say older instead of more. You could also leave out years.

(one?) Hundred participants (aged 18 years or older) were selected from each of the cities.