The guide says that it takes 18 days for a pet to grow into an adult, but I currently have a 26 day old adolescent that I really want to start breeding.
http://www.sylestia.com/view/pets/?petid=168449
I've noticed this before with other pets, but it didn't bother me because those weren't my first hatched tri-visual that could breed me more.
I'm not sure if this is a bug or if I'm just missing something, but there's a big difference between 18 ad 26 so I'm opting for concern. I mean, did I not click him enough as an eggling/hatchling?! -tears up-

....watch him grow into an adult at tonight's reset. -.-

@Yumi123,

The entire cycle is 27 days. It takes 18 days to go from an Adolescent to an Adult.

@Krinadon

Oh! Okay, so one more day. Could that be better stated in the guide? I've been here for quite some time and I always thought that after 3 days, the egg hatched; at 6 days, it became an adolescent; and once the pet was 18 days old, it was an adult. I'm rereading the text now and I have to really focus on the sentence structure to understand how it's actually meant.

Sure. I slightly edited the text to hopefully be less confusing.