People get really freaked out about training for their climb. It is normal, but calm down. There is no reason to worry if you train for it.
Yes, Kilimanjaro is a physically demanding mountain and yes, you want to be in shape. But you do not have to be superman to climb Kilimanjaro. A moderate training program is wholly sufficient. In fact, most people who hike regularly probably do not have to do much more additional training.
If you live in an area where there are mountains, you are fortunate. Take advantage of it by going on day hikes 2-3 times a week for about 2-3 months before your trip. Hikes that have elevation gains are the best workouts. Speed is not as important as stamina, as the walking on Kilimanjaro is at a very slow pace. So do not be concerned if you walk slower than other people. Building your endurance is the main objective here. Most of the days on Kilimanjaro you will hike no more than 5-6 hours, and that figure includes about 90 minutes of breaks.
If mountains are not in your vicinity, then train as much as possible on a Stair Master. Although you may look goofy, you should wear a backpack while you do this. You have to get used to carrying some weight. A pack with 15 pounds would be sufficient. Again, set the pace slow and go longer. Don’t go super fast for 20 minutes. This is not how to build stamina.
People who are not in shape currently should start their training a bit sooner, and add more exercises. Jogging will increase your lung capacity and oxygen absorption. Weight training will strengthen your legs faster. Overall, take it seriously and you will do fine.
The harder you train, the easier the climb will be.