@Mandrake-And-Karen0
You said you have only had five star ratings for the past three years, but that you received 2-3 lower scores in your first couple of years of hosting. From what I understand, and what others have mentioned, all of your ratings will be taken into account, not just the past three years.
It's impossible to calculate it without knowing the scores you got previous to the past three years, but as an example:
Say a host got 60 x 5 stars
but also 3 x 4 stars
The average would come to 4.95.
Of course, I am not saying you only got 3 x 4 star reviews in your first couple of years of hosting. I am sure that you got lots of 5 star ones too, but your average will not round up to 5.0* until you exceed an average of 4.995 or above (or it could be 4.996, I'm not sure). It is doable and it sounds like you are on track. It just takes a really long time.
I was at a 5.0 for the past 2.5 years, but a couple of recent low ratings mean that it will probably take me years to get back up to 5.0, if I ever get there at all.
Anyway, you can't know what your average should be unless you can factor in ALL your ratings from the beginning.