Is/ are followed by a number [closed]

Which is correct?

This month is 8 years since I stopped playing guitar.
This month are 8 years since I stopped plating guitar?

In all these cases, the actual or implied subject of the sentence is a period of time, irrespective of whether that period of time is one month or ten years. So, given that the subject is a [single] period of time - not a [multiple] number of days, months or years - the subject is normally singular.

I say 'normally' because there may be constructions where the subject actually becomes plural, although I cannot currently think of one!

I would add that, in many cases, the word "it" is included in the sentences and used to refer to the period of time, such as:

This month, it is 8 years since I stopped playing guitar.
Next month, it will be 8 years since I stopped playing guitar.

The use of "it" is shown in the answer from Bob Bobaloobob and the comment from Peter Shor.

The actual word "it" may be omitted, especially in speech, but it is nevertheless implied as the subject of the sentence. Thus, normally the verb should be singular, not plural.