On since/ago

A correspondent writes to ask whether it is possible to use sentences like I've been studying English since four years ago and Since three years ago, I've had several accidents.

It must be possible. The question wouldn't be coming up at all if people weren't being heard to use such sentences. What has happened, of course, is that there is a clash between the usage and the rule that is widely taught in grammar books.

The rule says that since and ago are incompatible, because since refers to an e...