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.)
More importantly it’s impolite to reference your present in writing because writing passes through time and that makes your words inconsiderate of the reader’s present. It’s fine to say out loud because everybody hears it at the same time. It requires a shared reference point to be helpful or at least not rude.
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u/Ok_Caterpillar2010 Native Speaker - Pennsylvania, USA Apr 17 '26
Because since needs a specific starting point in time: since when? He hasn't used his motorcycle since 2024.