It depends on who your great-grandmother is, when they were born and when you are born but the average age to become a great-grandparent is approximately 70 years of age.
The Gran Cavallo, or Great Horse, typically refers to the famous equestrian statue of Marcus Aurelius in Rome, which dates back to around 175 AD, making it nearly 1,850 years old. If you meant a different "Gran Cavallo," please specify, and I can provide more accurate information.
The Spanish word "gran" translates to "great" or "large" in English.
great = gran(de), magno, admirable, excelente Great Britain = Gran Bretana (with a tilde, the little wave, on the 'n' in 'Bretana').
gran/grande
great horse = gran caballo
great time = gran tiempo
Gran Reservas five years old (two in cask, three in bottle).
Gran Britania
gran nación
La gran cosa.
"My great love" in Spanish.
grande mamie.