Because Kilimanjaro is a marathon, not a sprint, you won’t need to trek as frequently as you may think. It’s a long and arduous road. However, if you are able, go for 2–3 hour treks. There’s a tremendous difference between walking for a long period on a level surface and trekking.
The major aspect of climbing Kilimanjaro that might be deemed “hard” or “tough” is altitude sickness. The thing with Kilimanjaro is that if you go slowly but steadily, you should be able to reach the summit without too much difficulty. Sometimes all it takes to avoid altitude sickness is a gradual ascent. You’re probably in for it if you’re attempting to get up there as quickly as possible.
You don’t have to be in great shape to climb it, but you must be healthy enough to perform the treks described.