I got my first muscle up at 45 YO having never trained for more than 6 reps of pullups. I was doing weighted pullups though so my case was probably a bit different than most. As Steve wrote a base of 10 bodyweight pullups before starting training for a muscle up is probably a good idea.
For some of your pullup training practice some high pulls, start by pulling to the chest rather than just getting your chin over the bar and when you can do that focus on pulling as high as possible (bar to the lower chest or further) and really work on that explosive pullup.
That being said a muscle up is really about technique, if you get a slight swing going and bounce out of an arch at the bottom it makes it infinitely easier than a strict gymnastic muscle up on rings.
This vid shows what I mean about bouncing out of the bottom position and goes on to explain the transition and the dip once you've cleared the bar.