Welcome to the forum.
1. Here are some URLs for you:
testosterone injections
testosterone pellets
2. The problem with both pellets and shots is that your testosterone level goes right up but then slowly declines so you may end up with a very high to very low pattern with accompanying symptoms.
3. The normal range for total testosterone is 300 - 1000 ng/dl. It fluctuates quite a lot, however, and is usually highest first thing in the morning. I have never seen a chart for "normal" levels based on age group because I doubt they have ever been firmly established. It's much more helpful to track your own testosterone level over time. Normal for you might be quite different than for someone else your age.
We have a lot of information about testosterone in our Andropause Center. You might want to spend some time there....
Hope this helps.