I began to learn mathematics at the age of nine.
The age difference between two people is fixed, because with the passage of time, everyone's age will be recursive year by year. Xiaoming's grandfather is 63 to 75 years old and has gone through 12 years, so Xiaoming should be nine years old, adding 12 years old equals 2 1 year old, so Xiaoming should be 2 1 year old at this time.