Honestly, no matter how long you've been domaining... Every year you'll back at the purchases of the previous year and realize your mistakes. This is because if you're a serious domainer you'll be constantly learning and improving.
It's the same thing with being a writer. Even if you stop worrying for a few years, you'll be better every time you write than the previous time (on average)... Because as people we grow and learn.
Our jobs as domainers is to try and shorten the time between the different skill level jumps by reading all the blogs, doing courses, studying historical sales figures, analysing data points, buying and selling and learning from our mistakes, speaking to our peers and learning from them, collecting and mastering tools, learning valuation methods, methods and places of gaining exposure, and if you can find a coach or mentor that can also jump you ahead a few years.
You want to move as quick as you can between these various stages:
My own definitions:
Newbie - no profits ($x to $xx)
Beginner - some profits ($xxx)
Intermediate - significant profits ($x,xxx)
Professional - an actual income ($xx,xxx)
Expert - an impressive income ($xxx,xxx)
World class - top of the game ($x,xxx,xxx)