I gather that Nobles can keep growing into their 20s, it also seemed that they have a slightly longer lifespan but not as much longer as the extended growth would imply. Odd when paired with their very young age of adulthood.
Its also interesting that it doesn't seem to affect the start of adolescence, its easy to miss due to all the main characters being very adult but I have met few 12 year old boys who care about girls yet.
The whole series only happens in a span of a few years, too. I think a few of them didn't age exactly right though.
Trice went from 17/18 at meeting Tor (estimated) to 21 (specifically listed I think) when she married Timon.
23 sounds about right, Tovey was a senior (so high teens when we meet him, likely a year or two older than Trice and 3 or 4 older than Tor.