It depends what kind of experience you mean. I started working in a 'classic' (i.e. windows desktops and Novell servers in a private WAN) network/systems support+admin role in 2003, moved into web development in 2006, and then gradually got more involved in ops again until about 2013-14, when I started taking on new clients directly (only the very first job was I an employee - in every other position I was essentially a contractor - initially through agencies and then directly invoicing the company).

The income question isn't as easy to answer - my rate varied a lot from roughly what I'd been contracting at for some 'mates rates' clients, up to nearly 4x the price for others - but as is expected it wasn't consistent. It's been a couple of years of pretty steady work at a reasonable rate so I guess the "TLDR" answer is 3-4 years.

Keep in mind, apart from the first 2 or 3 jobs I had (2x government and then one at a Telco) everything else has been 'remote', and I've been geographically remote (I live in Thailand) since before I started this business. I have no doubt this has affected the number of potential clients, but it sure beats commuting into a city every day.

I hope that helps and isn't too much of a ramble. Feel free to email me if you want to discuss it further, my address is in my profile.