I haven't climbed Everest myself (but have been at base camp and trekked the Himalayas). I have climbed for the past 10 years and have summited several 20,000+ peaks including Aconcagua and McKinley in Alaska and am pretty familiar with Everest.
1. You're already in suitable fitness from a purely physical standpoint (altitude acclimatization obviously notwithstanding)
Plenty of old, relatively out of shape guys climb/attempt Everest these days. The mountain isn't what it was before when only hardened Alpinists would dare attempt even the upper camps. The routes are standardized and Everest although tough is not K2 or Annapurna tough.
It's a money machine and some of the guide businesses will take on pretty much anyone who will give them the money regardless of prior experience/skills and do their best to drag their rich butt up the mountain, not saying this is a good thing but this is really how it is. Walking around basecamp myself 3 years ago I saw quite a few Westerners who looked like they shouldn't be climbing a sledding hill let alone the worlds highest peak.
2. In terms of preparation, start off by familiarizing yourself with technical/alpine climbing techniques and gear. Start with Colorado 14-ers, and progress to Mount Rainier, which is regarded as one of the best "Everest Prep" mountains due to its cost, location, and preparation for Everest in regards to glacier/ice/crevasse climbing. After Mount Rainier, I recommend higher elevation peaks like McKinley/Aconcagua or even other Himalayans if you can afford it, but imo after Rainier you are technically "ready" for Everest.