Wow, this would be best guesses as far as the early distances go since it has been so long... I was playing casually once in a while for many years before I actually cared enough to figure out what I was doing and try to improve.
100 ft - I could hit 100 when I first started
200 ft - Probably 2 months
250ft - Less than a year
300ft - About a year
350ft - ~2 years
400ft - ~4 years (not long after I started breaking 350)
450ft - ~11 years (maxed out about 500-520)
One thing to note is that once I broke the 400 plateau I stopped caring about distance and started focusing on other aspects of my game, and as a result my distance dropped off a bit again. I'm back to the 400-430ft distance range now but I honestly don't care
It'll come back.