Eh, it's just different marketing for different cultures/audiences--they're probably hoping to hit young teens/even older preteens (because some parents will let their kids get Teen-rated stuff) and at least for the states that would mean censoring stuff like Ringabel's outfit so no one freaks over that.

Though honestly I kind of like that the Western made Tiz 19? Like I really hope the Japanese wouldn't have made him more flirtatious toward Agnes because he was 19, and...now I'm kind of suspicious, seeing as Ringabel and Sage both refer to him as more of a 'boy' when he doesn't go along with their stuff. I kind of liked that he was 19 and his hormones work perfectly fine but he's just not THINKING about that much of the time because there's more important things to worry about!

At the same time, maybe his age isn't really a factor in how he acts in the JP version--I know another JRPG with a 16-year-old protagonist which had absolutely no issue in having him very obviously notice the heroine's figure at first meeting. (This is actually a visual gag twice. The first is more subtle--the second has a dotted arrow.) Though maybe they might have thought an older Tiz would pursue the relationship more? IDK. I just hope that if they'd made Tiz 19 all along he'd have still been...well, the way he is.