Which is it: "1½ years old" or "1½ year old"? [duplicate]
Solution 1:
If the entry is part of a classification:
That kid is a one-and-a-half-year-old.
If the entry is describing the age of the person:
That kid is one and a half years old.
Both of these work, and work similarly for whole numbers:
That man is a 50-year-old [person].
That man is 50 years old.