No.
Years can be measured in hundreds; a hundred years is a century.
Hundreds of millions of years
hundreds
people hundreds years ago used pencil and paper to measure
years or year's
No
No. "I have known him for 5 years." Would be more correct.
'Since the last ten years...' is correct, but is only part of a sentence.
No that isn't grammatically correct. You should say 'Though George didn't like the school, he studied in the same school for ten years'
It has been 5 years since you knew him.Read more: It_has_been_5_years_since_you_knew_him._Is_this_sentence_grammatically_correct
The correct spelling of the plural noun is centuries (hundreds of years).
The correct way is to write New Year's Eve.
Yes, this is correct.
No. It is a sentence fragment.
20-year warranty would be correct: 20-year is a compound adjective applied to warranty.
If you use the "had" it implies that you no longer know this person. I had known means I don't know now. I have known means that you may or may not know her now.
Years can be measured in hundreds; a hundred years is a century.