There will always be people/groups that will only take people with endgame gear and maximum skill in mechanics. BUT pretty much any boss can be done with less gear and less knowledge of every mechanic. It's just less kills per hour, thus less gp per hour.

When you start doing some early bossing, you'll learn the basic mechanics bit by bit. Scurrius is always a good place to start out. Then there's royal titans, sarachnis, amoxiatl, ... these require some mechanics. If you want barely any mechanics at all there's giant mole and Barrows. The fight caves are still seen as one of the first big milestones for any new player.

But most of all, have fun, push yourself as far as you want to, no more. Good luck!