Imma skinny guy and I want to get strong?!

Protein shakes may cause a lot of farting. That's why I avoid them.

5'6" 105 is really lanky, but you're in pretty good shape if you can do 20-30 push ups. So, here's what you do. You do sets of 15 push-ups, but you do 3-4 sets. Do 3-4 in the morning when you wake up, and 3-4 sets of 15 push-ups at night or in the afternoon.

Crunches: Do them in between your sets of push-ups. If you can do as many crunches as you can push-ups, you'll be in great shape and notice the difference within a few weeks.

Since you're such a small guy, I would definately NOT recommend football, hockey or any contact sport. Dude, seriously. I'm 5'7" 138, and I run. Running track and cross country was my sport in high school. I recommend the same for you. If you can run, that could add muscle weight to your legs.

Start off with just a mile, and do shin exercises so you don't get shin-splits. Use googe to look them up. "preventing shin splits" should yield good results.

I'm an athletic guy who would be very thin if I didn't exercise.

I was you when i was that age. Im
Now 36 and 15 stone. I say enjoy it when you can. Circuit training and a healthy diet but stick to them!! Your metabolisim will slow down but keep the training up as once it does your physique will be spot on. Girls hate fattys anyway mate lol

Personal experience

You are entering Puberty (or in it already) so work on your muscule development while your body changes from boy to teen to man. During Puberty, testosterone builds up and will alter muscle development, voice deepening, weight, height, emotions, etc. Yes diet and exercise are important during these next 3 years. As you get into your teen years, your pushup number will increase.

Weight training and protein shakes

you get stronger one day

dude... join a gym