In formal research, which is more correct, and why:
- the group of 40-50 years old
OR - the group of 40-50 year olds
In any case the phrase in bold is to be treated as a noun only, as in:
The middle group of executives, ie. 40-50 years old is well
balanced….
Without a range, the hyphenation rules I am used to would suggest "15-year olds" for instance. However "the 15-25-year olds …" doesn't present well, does it?
There are related questions here, but none that seem to exactly address this topic. Eg.
Pluralization rule for "five-year-old children", "20 pound note", "10 mile run"
The main difference perhaps is that I need to use ranges, which already use a hyphen.
Best Answer
If you are using it as a compound adjective or noun, as in your example sentence, it should be "40-50-year-olds".
If you are using it as a separate qualifier, as in BillFranke's suggested alternate wording, than it would be "those 40-50 years old".
Confusing, perhaps, but the general rule is that when any sort of counted "thing" is used as an adjective, the object of the count is singular. "40-year-old man", "3-mile run", etc. Making it a range instead of a single number doesn't change that.
But when a number and an object of that number are used "on their own", i.e. not as a compound word, the normal rules of pluralization apply: "those 1 year old", "those 2 years old", etc.