Hi! I'm still fairly new, so sorry if this is common knowledge.

I thought that pets were supposed to be adults at 18 days old? I have some that are over 20 days old and still adolescents.

Is this is glitch?

Nope. Sylesties become adults at 27 days. Hope this helps =^-^=

Thank you!

An to add on Some Species take even Longer to grow up then others

Just to delve a little deeper for you:

A pet's age is technically measured in points - points kind of represent the hours the pet has existed, but can be varied by nurturing, and can be random for tamed pets. If a pet is genetically tested, their exact age in points will be visible in their image code.

For example, I have a lighira that is still an adolescent. His profile says he's 18 days old. If I right click his picture and select "copy image location" (or something like that - it's different for different browsers), I get this:

https://www.sylestia.com/image_builder_pet.php?species=lighira&breed=sylesti&gender=male&gd1=KK&gd2=NN&gd3=AA&md1=NN&md2=NN&md3=NN&ec=eb590f&c1=fcbe1f&c2=7d0205&c3=f4661a&gd1c=850604&gd2c=830502&gd3c=d00601&md1c=510504&md2c=e3220a&md3c=4b0508&ac=f66415&maturity=461&costume=0&size=250&owned=1

I underlined the part that tells his exact age. Maturity is the most exact way of telling a pet's age! Pets you find in the wild can be at any number, so it can help to look at the maturity.
0 - 72 points: egg
73 - 215 points: hatchling
216 - 647: adolescent

Just remember that a pet has to be genetically tested in order to see its maturity!

Thank you very much!