Did this in Dec. 2011, with Peak Planet on the Shira route. I didn’t even plan on it, but i had two weeks vacation to use up and 15 mouse clicks later, I had a plane, hike and 3-day safari booked. It’s a challenge, but anyone in reasonably good health should not have an issue with it. Be sure to take a longer route to ensure that you have enough time to acclimate to the altitude (rule of thumb is 5 days = 50% chance of summit, 6 days = 60%, etc).
Watching the sun come up on the crater rim with a cup of tea keeping my hands warm was one of the best moments of my life. I don’t know if I’ve ever felt more alive then on my solo trip to Africa.