How long does it take to get good at guitar?

That all depends on YOU. Everyone learns at a different pace. Plus, the term "good" is subjective. One person's definition of "good at guitar" might be different from yours. Most beginners with no prior musical experience tend to pick it up within an average of 3-6 months. If you practice consistently on a daily basis, you're going to progress much faster than someone who only practices once or twice a week for 30 minutes. Ask yourself what your definition of "good" is. What do YOU want to accomplish on your guitar journey. Start there.

When will my fingers to stop hurting?

Again, this depends on YOU and how consistent you practice. The more often you practice playing guitar, the faster the pain will subside. You're basically pressing your soft, fleshy fingers into steel strings. Yes, it's going to hurt at first. But, you will develop callouses over time that will make you immune to the soreness you are experiencing now.

How often should I practice?

As often as possible. Daily, if you can! Make it a habit. I recommend at least three 30-45 minutes practice sessions a week. If you need an off day in between, take it. But, don't go to far in between practicing. Your goal is to build those callouses! Even if you can just fit 15-20 minutes in between, it counts! Everyone has the time no matter how busy you're schedule is. It comes down to whether you choose to make the time for it.

What if my fingers are short? I heard it's harder to make certain chords.

We're going to bust this myth right now. There are a ton of super talented guitarists out there who have no problem playing barre chords and the more difficult chord shapes. It's all about finding a way to adapt yourself to the instrument + finding a guitar that suits your body. If your fingers are more on the shorter side, you may want to opt for a guitar with a narrower neck. You may even want to check out some 3/4 size guitars as well if you want a smaller body.