My pets, unless massively nurtured, have always taken around 8 days to reach adolescent, fabled or normal. If you really want to know, pay attention to the maturity level in the URL. I had one recently grow up and it's maturity level is 221, while one right before that is a hatchling and its maturity level is 200. So somewhere between that is where it reaches adolescent. You can find this maturity level in the Image URL. Right click an image and either copy the image url or open the image in a new tab to find said URL.

https://www.sylestia.com/image_builder_pet.php?species=lupora&breed=sylesti&gender=male&gd1=NH&gd2=NB&gd3=NG&md1=NN&md2=NN&md3=NN&ec=a16313&c1=eaedec&c2=563746&c3=dafae4&gd1c=3a5950&gd2c=6f6e68&gd3c=dce0e3&md1c=ebdbda&md2c=b06680&md3c=9c6276&maturity=221&costume=0&owned=1&size=250

ok thanks! i'll keep this in mind because the Griffi grew up so it might have also been what Imperium said

Could be. I think the maturity level is 216 because I had a boy grow up (I guess he had more clicks) and he's at 216 and the 200 girl from before is at 212. I changed her maturity lvl in the url ro 215 and she was still a hatchling but when I changed it to 216 she went to adolescent. But what Imperium said is also true. Lol.

On a similar note, what is the youngest age at which you have seen a pet become an adolescent or an adult?