Queen pulls out of Commonwealth event

The Queen returned to public duties after a hospital stay, attending a Commonwealth Day reception where a new 16-point charter was signed. Earlier, the Duke of Edinburgh represented the monarchy at a service in Westminster Abbey. The Queen, who has missed the event only once before, is expected to continue her engagements, indicating her return to full health as she approaches her 87th birthday.

What is the Queen's age as mentioned in the text?

What health condition caused the Queen to miss the Commonwealth Day event in 1993?