Sure.
Baby born when parents are 18. In 36 years, the ratio is 54:36 = 3:2.
Baby born when parents are 19. In 38 years, the ratio is 57:38 = 3:2
Baby born when parents are 20. In 40 years, the ratio is 60:40 = 3:2
Baby born when parents are 21. In 42 years, the ratio is 63:42 = 3:2
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Baby born when parents are 30. In 60 years, the ratio is 90:60 = 3:2
Baby born when parents are 31. In 62 years, the ratio is 93:62 = 3:2
Baby born when parents are 32. In 64 years, the ratio is 96:64 = 3:2
Baby born when parents are 33. In 66 years, the ratio is 99:66 = 3:2
So there you have 16 possibilities that can give you the ratio of 3:2 ,
for parents having a child when they're 18 or older, and living to less
than 100.