Yes, when used as an adjective.
Year-to-year is hyphenated when used as an adjective: year-to-year comparison, year-to-year budget.
Year to year is not hyphenated when it is used as a time period: We come back to this same beach year to year.
Hyphens not needed
Most people would spell it sixteen-year-old child. But over the last 20 years, people are ignoring the hyphens.
No. Use hyphens when creating a compound adjective, for example a two-foot width or a four-foot depth.
hyphens
I really doesn't matter, but if you're writing an essay or something, keep all words that can have hyphens, either wil hyphens or without them. My point is that you want to be consistent.
Hyphens not needed
Yes it should.
no hyphens - 57 years old is what you are.
Yes it should be hyphenated.
Yes, "year to date" should be hyphenated when used as a compound adjective before a noun, as in "year-to-date performance." However, when it appears after the noun, such as "the performance year to date," no hyphens are needed. Always consider the context to determine the correct usage.
Yes, you should use hyphens in "eleven-year-old" when it functions as a compound adjective before a noun. For example, you would say "an eleven-year-old child." However, when using it as a predicate adjective after a verb, you do not need hyphens: "The child is eleven years old."
If you're using the phrase as an adjective (example "This easy-to-use remote is great!") then it will definitely need the hyphens. Otherwise, the hyphens are incorrect.
If you're using the phrase as an adjective (example "I hate the end-of-the-year audit!") then it will definitely need the hyphens. Otherwise, the hyphens are incorrect.
Most people would spell it sixteen-year-old child. But over the last 20 years, people are ignoring the hyphens.
Yes, "year after year" should be hyphenated when used as a compound adjective before a noun (e.g., year-after-year performance). However, it is not hyphenated when used as an adverbial phrase (e.g., they met year after year).
No, you should not.
There are no hyphens in the word ago.