Barnabas I'd put in his mid-twenties, though he definitely didn't look it. The primary reason I'd like a Julia older than Barnabas is that I quite enjoyed Julia's obvious irritation at Barnabas chasing after the SYTs when he was so obviously aware of her affection for him. If Julia was younger, that could possibly break that dynamic when Barnabas gives up on finding Josette, as then, if Barnabas had a younger woman so clearly lusting after him, he'd probably jump at the chance to bite her. Of course, should that be ignored, a younger Julia could still think, "Why? I'm not much older than them. Why them and not me?"