The Simon in CVJudgment is the Simon from 'after' the events of Simon's Quest.
It's likely that he's 22 during Simon's Quest, and 23 during Judgment.
That means he'd be a teenager (16 from Judgment, 15 from Simon's Quest) in the original CV when he faced Dracula for the first time. But I guess that's correct since in the story of Belmont's revenge, Soleiyu came of age at 15 in terms of being ready for official vampire hunting. For Simon though, talk about Trial by Fire.
I take Judgement as "canon unless it contradicts something from other game". Since nothing really does, i take it as canon
There is the nonsensical love triangle between Grant, Trevor, and Sypha that was non-existent in the original CV 3 game. Like I said before 'Best to take anything from Judgement with a tremendous helping of salt.'