Description is not enough.
age p for the person making the description
age v for the great-grandmother
PEOPLE AGE
First Person p
Mother p+4p=5p
Grandmother 24+(5p) and 24+5p=v-40
Greatgrandmother v
Not possible to exactly find age of any of them.
Notice there is ONE equation in two variables. A reasonable example for p could be p=5 for First Person. This will give:
Mother is 25
Grand Mother is 49
GreatGrand Mother is 79