Generally speaking it is not necessary to capitalize decades unless it occurs at the start of a sentence.
You do not have to capitalize fourteen hundred dollars. The only time you would capitalize any word in that phrase is when the word "fourteen" was used at the beginning of a sentence.
There are 10.6 decades. Or 10 decades plus 6 years.
70 decades
There are 100 decades in a millenium
I see no reason to capitalize it. In general, you capitalize something if it is the name of a single, unique thing (for example, the name of a person or country); or if something is considered sacred or otherwise important. There are a few additional cases when you capitalize something, but I don't see how any of them would apply in this case.
In "Yours truly," you capitalize the first letter of each word if you are using it as a complimentary close in a letter, as it is a formal sign-off.
no, but you do capitalize mum
You capitalize the first A but not the last a.
You capitalize proper nouns.
No, you do not capitalize the word drama.
You capitalize Huntington
do you capitalize the word protestant
do you capitalize roaring twenties
When it is the name of a particular country, you capitalize it.
Capitalize challah bread
You would not capitalize it. cotton gin
4.5 decades equals 4.5 decades!