The example you provided, "He is younger than I ,"could indeed be used in Swedish, and it would be understood to imply "He is younger than I am," even without explicitly stating the verb "am." This is because Swedish, like many languages, often relies on context and implied meaning. So, to answer your question, it's not so much anexception to the rule in Swedish grammar as it is a difference in how the languages handle pronoun cases and implied verbs. The flexibility in Swedish pronoun use might seem like a misuse from an English perspective, but it aligns with the Swedish language's own grammatical standards and practices.

@@aymanmosbahi149 Thanks for the reply. Much appreciated. In English, the same is true, in that anyone would understand what the speaker meant, even if the wrong pronoun was used or the additional verb was dropped. But it seems in both cases that it's technically incorrect, but the listener learns to adapt to the incorrect grammar. I figure that must be the case. Otherwise it would be documented and taught as part of the language. But I've found no evidence of this quirk in any official material, leading me to assume it's just common slang, but in no way official Swedish. 🤷‍♂️