NZ has a requirement that one has done an advanced first aid cert. There are courses tailored to sailors. The ocean one covers 2 weekends and is good but in practice one would need to refer back to the course material or a reference book.
It might seem overkill but if you are out of helicopter range and say four or more days from land, and perhaps more so in an older age group there is the possibility of some intervention being required.
Book learning is all very well but it requires testing to see if you pick up the key things. Also hands on teaching is desirable for say CPR to see just how much pressure is required and how hard it is to sustain. Similarly doing stitches and giving injections requires some practical experience.
In a marine environment issues such as keeping a MOB flat on recovery and getting someone into a safe position first come into it. You also need a decent medical kit and gain the right to have and dispense drugs.
Older people incidentally may find that a thousand on a portable defibrillator may save a life if not theirs someone in a neighbouring boat.
Such a course is required for many marine qualifications so is likely to be found in most countries.
It is first aid, rather than selfcare or safety which are important but different areas.
I suppose some would see all this as overkill, indeed and hopefully one may not need it but apart from being at sea in many islands for instance medical supplies or care would not be available. A SSB and VHF radio would also be helpful, there may be a dr or nurse in the next bay.