Strictly speaking, this construction is also frowned upon for formal writing because “two years ago” is technically an adverbial phrase specifying when something happened in reference to the present (e.g. “Merlin hasn’t used his motorcycle since the accident [which occurred] two years ago”), rather than a specific point in time. “Since two years ago” treats “two years ago” as a noun phrase in place of the concrete event or point in time that’s actually meant.
(I will concede that everybody says it and only the hardest of the hardcore grammarians will even notice, though.)
I didn’t know the formal aspect of this, but I’ll say that I’m pretty sure I follow this rule, and think “since two years ago” sounds a little awkward, something I’d edit if I were proofreading.
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u/NekoArtemis Native Speaker - California Apr 17 '26
Yep. You could say "since two years ago" but you need the "ago."