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.
4
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
the great earthquake of
great horse = gran caballo
great time = gran tiempo
Gran Reservas five years old (two in cask, three in bottle).
La gran cosa.
gran nación
"My great love" in Spanish.
grande mamie.
Gran Britania