off road chiming in here.... more power too you if you are trail riding on a CX bike! There are no rules other than what Dogmama posted. Speed is variable, you shouldn't use it as a guage unless you are training for racing.
My trail rides vary from 23 mph on certain climbs to 19 mph on certain descents, or more. Lots of variables. I have one local single track loop that's 12 miles that I ride in 65 minutes, another that's 8 miles that takes me two hours, it's much more techncial with really big climbs. If your guy is pushing you for speed and you arent there yet, tell him to back off or find some new riding partners.
For mountain biking, I guage progess by comfort level on the trail, speed, and how well I handle techical stuff.
Irulan
2015 Liv Intrigue 2
Pro Mongoose Titanium Singlespeed
2012 Trek Madone 4.6 Compact SRAM