When he was growing up, the father of basketball superstar Pat Riley forced him to play basketball with kids who were stronger and tougher than he was. He said it forged his son into a winner. I can see the principle at work, but it doesn't come naturally to me. In my efforts to provide you with the parenting you missed as a kid, I've always preferred a gentler, more nurturing approach.
Nevertheless, the time has come to override my personal desires for the sake of your character-building needs. I recommend that you force yourself to play with grown-up kids who're stronger and tougher than you.