In reply to kenr:
> 4 days a week is the most someone 55 and older should climb and expect to get optimal improvement benefit.
I don't think you can make hard and fast rules like that because climbing is so diverse. I also think optimal improvement for those who haven't been climbing that long is more likely to come from learning technique and skills rather than strength gains.
> Serious Rest time is critical for muscles and tendons to _grow_
I agree with that but only in situations where someone is first really stressing their muscles and tendons. Climbing, particularly stuff like limit bouldering, campusing etc. can be brutally hard on the body. However the way most climbers practice I think it's mostly a fairly gentle sport, especially when practised with good technique. Most people fail because they can't see how to do a move or are a bit scared to go for it above gear. These two things naturally limit the amount of physical stress on the body.
I think it's misguided to think of a fixed amount of rest per week, without taking into account what someone is actually doing. Sure, if he was training on a Moonboard, your suggestions might be a good ballpark figure. But if you look at Johann's profile you'll see what he's doing is top roping routes of around 6a. In terms of the amount of effort, exertion and sheer physicality, a Moonboard climber is essentially doing something completely different.
Someone posted on here several months ago that they had just completed their 500th day of climbing in row. So it's perfectly possible to climb without rest days for a long time without getting injured. It will depend on what you're doing, how hard you're pushing yourself physically, and how much volume you're doing.