We dunno, its said 20 something years ago, and there were hits in one of the authors post that Enzo is likely older but they deleted it immediate saying they want their relationship to be something where age doesn't matters or something. But I think Enzo being older or younger both will be fun on its own way.(⌒▽⌒)
I said 25-26 because he got the back scars when he was 6 and he doesn’t look like he would be any younger than 5 in the flashback, so he probably got them shortly after meeting his grandfather. The flashback is also solidly 20 years in the past.
I can’t see Lorenzo being older than Rian tbh. Rian himself doesn’t come off as being that young.
He is a bit younger, it seems, probably 24-26. How Hanse's been keeping them equal, we should have guessed there wouldn't be much age difference. I thought the AU was a hint that there is a big gap, and also Enzo's attitude and lack of profile. I mean, if he's been active for years, there has to be something about him going around. Anyway, 2-3 years makes more sense, equality-wise. And now, I think the AU is more about that shadow thing.

Lorenzo as a kid IS SO FREAKING CUUUUTE.