Obviously this is 100% dependent on your genetics, but let's use me as a test.

My father was 6'1, 160lbs.
My grandfather (on my fathers side) was 5'11, 150lbs.

My grandfather (mothers side) was 5'5 5'6, 135lbs
My mother is 5'4 120lbs.

I am 6'0, 185lbs

If I do not lift and diet hard, I am 150-155lbs.

How much can I honestly grow? Can I hit 220lbs naturally? will my body even let me do that?

How much muscle can one gain over their 'natural' weight??

Everyone in my family is extremely lean, I guess I come from a long line of ectomorphs

I am already 25lbs heavier than the largest male in my family, and 50lbs larger than the smallest.

When will my genetics 'limit' my actual growth? There has to be a point somewhere, where it will stop.