As already stated, ( Thanks ALON ) counting scutes is not a true way to indentify age in boxies. They will add a ring each time there is a period of rapid growth rather than each year of life.
To determine a boxies age one would need to section a piece of their hind leg bone. You and I would want to pass on that.
Pyramiding is not related to determining age; but to improper growth of the boxie's scutes due to poor diet, lack of UVB lighting, or a combination of both.
Very old boxies will have worn off their rings and appear to have a smooth carapace. The geographical area, and hardships endured by each individual boxie affect how fast their shells become smooth. If you can barely see faint rings; I would guess that your boxie is between 40 & 50 years of life.
Ric