I have had to bail a few times due to injury but I have gained 60-70 pounds of muscle since my first cycle 18 years ago. If I didn't have to start over twice that would easily be 100-140 pounds. There is no reason you can't average 7-10 pounds a years. Your first year will be the biggest because you are smaller and have more room to grow. But after that you can keep growing without sliding back. You just haven't been doing it long enough to know that. or to know how.