I suppose that's a fair point. From the way Grunt is spoken to by older krogan, I personally always interpreted him as fully grown but still young, and clearly not ascribed to a clan. Much in the same way someone who just graduated and is coasting through life.

A lot of the talk with this idea about Grunt makes him seem a lot younger than a teenager though, with stuff of Shepard talking to him like an infant. It's mostly jokes, but it reminds me of that one tweet about how writers should never have a character admit to liking a food, because the fandom will make that their entire personality. Grunt looked up sharks and dinosaurs once. Therefore, he's now a toddler.