I have a question about a grammar point, not covered in any grammar-related book, that is difficult for non-native English speakers. I would be so grateful if you could briefly explain why the following sentences are correct or incorrect:
1. I haven’t seen Ali since two minutes ago.
2. I haven't been to London since two years ago.
Specifically, my question is about the construction of “since ... ago”, which many English teachers in my country believe is correct. They say a continuative perfective describes a situation that started somewhere in the past but continues into the present and, probably, beyond. That is the case here. Such a continuative perfective may, but need not, be accompanied by an adjunct introduced by “since”:
Subject — Continuative Perfective — “since” [starting point in time].”
The continuation is expressed in the “since,” and “two years ago” or “two minutes ago” is as good a starting point as any.
However, I believe that native English speakers would not use this construction but, rather, would follow “since” with a specific point in time such as a year, an exact date or a reference to an event. “Two years ago” is a period of time, not a specific point in time. To make my case, I need solid justification. Maybe it is a question of idiom rather than grammar. I know that spoken English can be either formal and structured or casual and informally structured, and I tend to prefer an approach that follows a formal structure without excluding informal and slang usage, where relevant.
P.S: I do know that there is nothing wrong with “I have gone to school since 2009, ten years ago”. Syntactically, it is different from the sentences #1 and #2, in that “since” and “ago” are now in different phrases: “ago” has been shifted to an afterthought. But in the sentences #1 and #2, “since” indicates a period beginning in the past and continuing into the present. Whereas “ago” concentrates on that beginning in the past. It is this that makes the construction uncomfortable: one word highlights the continuation, another focuses on the past.