So, I've been told that maturity and age are not the same thing (if you use magical pie on a pet, it doesn't increase the age). How do I see the maturity then? The person said that you cannot, unless you look at the pet's URL, but i don't get how can I see the maturity from the address bar.

It's not the url of the pet, but the url that is linked to the image address. You have to copy the image url and post it or open it in a new tab and the maturity should be listed close to the very end of the address.

Thanks )

Just to add to this, the maturity hour by hour will not show unless the pet is tested. If its not tested, the maturity will only show as the minimum amount for the current status: 72 for hatchlings, 218 for adolescents and 648 for adults.

Example check of the URL (I've bolded and highlighted and the relevant number in red):
https://www.sylestia.com/image_builder_pet.php?species=ny%27vene&breed=sylesti&gender=male&gd1=NN&gd2=NN&gd3=NN&md1=NN&md2=NN&md3=NN&ec=f9054d&c1=130807&c2=330404&c3=5f090d&gd1c=2a0f16&gd2c=e50431&gd3c=040706&md1c=e40b32&md2c=080b08&md3c=c90805&maturity=119&costume=0&owned=1&size=250

Thanks for the info )