The average of the guys I have shot with over the years is probably around 19-20. You will have a couple guys that don't miss and a couple that can't hit their own backsides with a road map, but most are high teens and low 20's.
I wanted to be a trapshooter a couple years back, so I went out and traded for a trap gun blah blah blah. I had been able for a couple years to walk out on the line and shoot a 21-24 anytime I wanted while only shooting 10-15 rounds a year. I wanted to shoot better so I went to work at it. I got up to a whole whopping 23 average from a 22.5 LOL. Never did run a 25 while I was "trying", and gave it up after about 6 months and even traded off the gun. I just do not enjoy shooting on the line with self proclaimed "serious" trap shooters, I like to talk and have fun on the line and most find that unacceptable behavior on the line.
I am able to go out now and shoot a 23-25 from any yardage, even while only shooting 6-10 rounds a year. The point of my cheesy story ^^^^^ is that you can work entirely too hard at improving. It was not until I was able to relax and put what I had learned in my practice into effect that I improved drastically. Most of my 25's are from 22 yards and farther back, it slows the hard angle shots down just a hair for me and I hit them harder. #1, you have to relax or you are going to have a hard time. #2, you HAVE to have fun while shooting. So go out and enjoy trap, try to shoot with a squad that is a little looser, the "silence or else" crowd is not a lot of fun for most of us.
The shot that was my downfall and still is really is the perfect straightaway, I expect to just crush it and get lazy. If I miss it will be 3 to 1 odds that it was a straightaway.
Go out and have fun, shoot a little skeet too, it will help quite a bit on the hard angles of trap.