At what age do you recommend replacing each of the above?
That really depends on a number of factors. Most important probably being locale and whether or not the boat is sailed on salt water.
As was mentioned earlier in this thread, great lakes or other freshwater boats don't have nearly the corrosion problems that salt water boats have. Also, the more tropical the climate, the bigger problem corrosion seems to be.
But also, maintenance plays a part. If chainplates have been leaking, that would certainly accelerate their degradation and cause them to need replacing earlier than one's that have been kept dry.
If stuff isn't rinsed off after being bathed in salt water, it's going to corrode quicker.
I'm speaking mainly of cruising boats here too. My partner, when he was racing, would replace his rod rigging every five years. Those racer's can really stress a rig.
Whereas I've seen rod rigging on cruising boats that was twenty years old around here and that still looked good. (I still think that's way too old and told them so).
So, to answer your question directly. In this area, Tampa Bay, I recommend thorough and regular standing rigging inspections starting at 10 years and replacing standing rigging between 12 and 15 years regardless of what the inspection reveals. The same for stainless steel lifelines.
Chainplates are a trickier proposition. I usually always recommend inspection at the time of re-rigging, but the thing is that they need to be removed in order to inspect them properly. And if you go to the trouble to remove them, then in my opinion it's a bit silly to put the old one's back even when they look okay. They usually aren't all that expensive to fabricate so you might as well replace them and the bolts and sleep better at night.
Hope that helps.