181. Correction: years
Generally speaking, we have two choices here:
for many years
many years ago
In other words, we cannot use for and ago together.
Want to know why? Sure you do! It's simple!!
When we have a preposition and a noun together, we have a prepositional phrase. A prepositional phrase is actually one kind of adverb phrase. Are you still with me? We're almost there! So, when we use for and many years together, we have an adverb phrase, right? Right!! Now, ago is an adverb, right?? Right! Therefore, it is redundant (unnecessary) to use ago with the prepositional phrase. Easy, right??? Right!!