It's in fine fettle right now.
Prince Harry remarked recently that the Queen needs to go easy on her duties, especially now that her husband is in his nineties. The Jubilee royal tours have therefore been spread out between the four senior royals - the Queen stays put in the UK, the Prince of Wales goes to Canada and Australasia, the Duke of Cambridge goes to the Pacific, Prince Harry goes to the Caribbean.
The Queen Mother lived to the age of 101. Her daughter Queen Elizabeth II is in excellent health, does not smoke and leads an active working life. It is quite possible she could live as long as her mother, which means we have a sovereign monarch aged over 100 celebrating yet another diamond jubilee.
When the Queen is 100, Prince Charles be 77. He is already the oldest ever heir to the throne, having just overtaken the previous record held by King Edward VII. It is quite possible he too will not be willing to take on too much, and his wife must be getting weary of royal duties taking over what's left of their lives together.
So Prince Harry's statement must be an indication that we are going to have a communal family regency for a while, while the old people sit on the throne, but the bulk of the work will be done by the younger royals, most notably Princes William and Harry and their respective wives.
Charles's reign would be a short one, and Prince William will probably be crowned King when he is about 50. William is already nearly 30. King George VI was 40 when he came to the throne, King George V was 44. Queen Elizabeth II was 25, and Queen Victoria was 18.
All of this depends of course on the successors living. If an Argentinian nutcase downed William's helicopter with him in it, and Harry gets killed in action in Afghanistan, and Andrew does not outlive Charles, then we could yet see one of Fergie's girls on our banknotes, complete with Pretzel crown.
It is therefore in the royal family's interests for Kate to have a baby as soon as possible! I do hope they've got some of William's sperm frozen as an insurance policy.