I gotta wonder about the uppermost size of a maturation chamber before the Borg just say "F*&k it." (Thinking about dinosaurs and leviathans. Smart ones, mind you.) or if a species might age so slowly that the Borg would avoid them as children (It's conceivable that Vulcans mature three times slower than humans, that a FULLBLOODED Vulcan (I suppose T'Pring and Ston were the same age as Spock and they all looked kind of the same age, but but no one tried to enforce the arranged marriage on T'Pol until she was nearly 60, however T'Pau on Enterprise was said to be 30 and the actress was way too hot to be thirty (I'm over thirty.).) in their 30s would probably look like a human teenager.
And for the other races who mature even slower than that?
To my recollection, Vulcans mature at a similar rate as Humans do.
It's just that their lifespans are about 200 years compared to humans in the 23rd and 24th century (around 140).
Other races exhibit this kind of biological structure as well.
Klingons for example mature apparently faster than humans and also seem to exhibit longer lifespans.