I'm a skinny 17 year old male who's started doing calisthenics. How long would it be til it shows some visible results?
If you're dedicated and train hard - you'll see some results in 1–3 months.
Focus on Deep Knee bends/Bodyweight Squats for high reps - this is a classic exercise that's been used for centuries by wrestlers and athletes to build muscle, strength and stamina.
Various forms of pushups and pullups will hit the upper body nicely. Use different hand spacings and build up your reps.
Finish off with wind sprints or hill sprints.
After 8–12 months, you'll DEFINITELY see a difference.
After that, you may want to shift to weight training, because now that your body is conditioned to physical exercise, the gains will be pretty dramatic.
**NOTE - you will need to eat A LOT, to build muscle mass. You can't build muscle on a diet, especially if you have a fast metabolism. That's one of the basic mistakes that skinny trainees make, they don't eat enough food, especially protein, to recover from physical exercise and build muscle mass.