Am I too old to start learning how to play the guitar?

Not as long as you have the ability to pick up the guitar, willingness to learn and time to practice. Adult student may run into some complications learning, but it's not because of age. Most times people think that younger people learn faster simply because they are young. In my experience, that is completely NOT the case. Younger people learn faster mostly because they don't have any preconceived ideas about how everything should be learned. They are not subject to getting carried away with looking for the finish line, they are simply  having fun and enjoying the journey. 

How many times a week should I need to practice AND how long should I practice?

It depends on how quickly you want to get better and how much time you have to dedicate to guitar. I firmly believe that everyone should have a solid balance between your musical and non-musical activities. In our current world, people are busy, they have school, careers, families to take care of, friends to hang out with and hopefully other hobbies. Having said that, I generally tell my students that if you practice at least 30 minutes a day, 5-6 days a week that they will see solid progress. Notice that I didn't mention that the 30+ minutes have to all be done in the same block of time. With a well structured practice schedule, you will have the ability to "break up" your practice throughout the day. I've seen far too many students who will skip a full day of practice simply because they didn't have a solid block of time to practice. Never let that slow down your growth. 

Why do my fingers hurt?

When you first start playing guitar, your fingers are going to hurt and become tender from pushing down the strings. There are a couple of things that will make that happen less and less as you continue learning. The first thing is that you will begin to develop callouses on your finger tips. As the skin on your fingertips begins to toughen up and become thicker, your fingers will hurt less and less. A couple of things about callouses. If they look like they are starting to peel, leave them alone. If you pick at them and tear them off, you will have to start all over again. the second thing that will help your fingers stop hurting is the amount of pressure that you use to make notes. As your technique start to come together, you will start to realize that your fingers have become considerably stronger and that you no longer have to try and crush the string to make a note. Start playing with minimal pressure and tension and that will allow you to play longer and not have to stop playing because your fingers hurt. 

How long will it take me to get really good or play like {insert famous guitarist's name here}?

The amount of time depends completely on how much and how often you practice. It also depends largely on how efficiently you practice and whether or not you are practicing in a structured way. As far as how long it will take for you to sound just like you favorite guitar, it will never happen. I'm not trying to be negative, but when you take into consideration that the way a musician sounds and his/her tone is built by life experiences, years of practice, the influence (good and bad) of other guitarists, how he/she learned to play and the other factors, no two people are the same. Besides, when an expansive subject like music, you should never try to look for the finish line. You should just enjoy the journey and the small day to day victories. As long as you try to play better today than you did yesterday, you will get better and have a better experience learning music.