Yes. Most people on the mountain right now have never climbed anything before. That part of the sales pitch is true.
What you genuinely don't need
Ropes, harnesses, crampons, ice axes, a course, or any previous mountain. Every normal route up Kilimanjaro is a walk. There's one short scramble on the Machame and Lemosho routes, the Barranco Wall, where you'll use your hands for balance on what's really a rock staircase. People who worry about it beforehand almost always enjoy it, and nothing about it is exposed in the way the photographs suggest.
What you do need
The ability to walk five to seven hours, day after day. Not quickly, because the pace is deliberately slow. But six days in a row with nothing waiting at the end except a tent, and then a summit night that starts around midnight and runs twelve to fifteen hours.
A tolerance for being uncomfortable. It's cold, you sleep badly, there's no shower, the toilets are what they are, and above 4,000 metres you'll have a headache more often than not. People who've done it usually say the walking was easier than expected and the grind was harder.
Honesty about your health. Heart and lung conditions, pregnancy, recent surgery and some medications all matter at altitude. Talk to your own doctor, and tell your operator what they said. Nobody on the mountain can diagnose you.
How old is too old, or too young?
The park sets a minimum age of ten, and children above it need to be genuinely willing rather than brought along. At the other end there's no maximum, and people in their seventies summit every year. Age matters far less than pace, days and attitude.
How fit is fit enough?
If you can walk six hours over hilly ground with a daypack and finish tired rather than broken, you're in the right territory. If you can't do that yet, you've got a training target, and three or four months is usually plenty. Being very fit is pleasant but it doesn't protect you from altitude, and it sometimes works against you, because fit people walk too fast.
The thing beginners get wrong
Booking the shortest route. It's cheaper, it fits the holiday, and it's the one choice that most reduces your chance of standing on the top. If you're new to altitude, buy days before you buy anything else.
Which route suits a first-timer
Lemosho over seven or eight days is the usual recommendation, because it has the gentlest profile, a built-in high-then-low day and some of the best scenery. Machame over seven is the other good answer and is busier. Marangu is tempting because of the huts and because it's cheap, and it's the steepest learning curve on the mountain for someone with no altitude experience. The differences are set out on the routes page.