"Size matters" is a subjective statement and depends on what context it is being used in. In terms of calisthenics, size can play a role in certain exercises, such as pull-ups or muscle-ups, where having a greater strength-to-weight ratio can be advantageous. However, calisthenics is not solely focused on size, but rather on building strength, endurance, and control using bodyweight exercises.
As for how to start calisthenics, it's important to begin with the basics and progress gradually. Start with exercises that you can perform with proper form, such as push-ups, squats, and lunges, and gradually increase the difficulty by adding variations or increasing reps/sets. It's also important to have a balanced training program that works all muscle groups and includes proper warm-up and cool-down routines.
There are many resources available online to help you get started with calisthenics, including tutorials, workout plans, and progressions. Additionally, finding a supportive community or coach can help keep you motivated and provide guidance as you progress