Looks like a Testudo graeca ibera
Wow, 15-20 years old?!? Did you have him since he was a baby? How big is he now?can you show a picture of him? I’m also curious as to how big my tort is going to be so that I can prepare for his future enclosure. I am just so happy I did some research before I got him coz I definitely am not in a position to take care of a bigger specie of tort just like the sulcata even though they’re popular here. So happy I got a greek which stays relatively small but is friendly and has a great personality.I'm still struggling to identify the subspecies of my Greek and he is approx 15-20 years old!
It can be really tough as there are 12 common and some sources say as many as 20 subspecies. You may have to wait a bit to determine subspecies and definitely sex.
The Greek Tortoise Care Guide (Testudo graeca ssp) Chris Leone HermanniHaven.com GardenStateTortoise.com theTurtleRoom.com THIS CARE-SHEET IS DETAILED FOR A REASON. READ IT THOROUGHLY BEFORE PROCEEDING WITH OBTAINING A TORTOISE. Moroccan tortoise (Testudo graeca marokkensis) Introduction...www.tortoiseforum.org
This guide has a info on each subspecies, but the coloration of the skin and shell will probably change as your tort ages so it will be tricky at best.
Sorry cant be more helpful. Good luck.