When he lifts the leg to kick, you can lift the leg to kick his supporting leg or groin or shin area. Then step in. Youth vs. Age, Small vs Large With age your body deteriorates. You cannot rely on muscle power. You must rely on position and sensitivity.
Every opponent has weak points.
You must find the weak points. A larger opponent does not have the advantage with position and sensitivity. With protection, the larger opponent will win. Brute force methods have the advantage in this case. For Wing Chun, it is more fair on the street with no protection.