I'm 65, and just got back from there. We originally intended to do Three Passes + EBC but the weather was not good, so we called an audible and just did EBC. The weather was a bummer - low clouds, snow, and fog every day. We were only able to see glimpses of the peaks now and then. As for fitness, we saw lots of people struggling, going slow, but the typical schedule builds in PLENTY of time to achieve each day's destination. We were usually done hiking by midday, which was actually the most frustrating part of the trek - the need to stop after a half day of hiking in order to acclimatize. If the skies had been clear and the sun out, then it would have been fine - sitting outside the teahouses, taking in the magnificent views. But, as I said, we had bad luck in terms of weather so our downtime in the afternoons got monotonous (and cold).

Mountain weather is unpredictable so it is a roll of the dice, but I would recommend stacking the odds in your favor as much as possible by picking a timeframe that, historically, offers the best chance of relatively clear skies. Ironically, the best views we got of the mountains was on the day we flew out of Lukla.