In my country, anyone above 18 years has the legal right to gamble but I think that people with the inability to control emotions or who have been diagnosed with high BP should be prohibited from gambling because gambling affects emotions and a person with high BP might easily have a crisis because of shock from losing in gambling. Losing is indispensable and so, individuals who cannot control their emotions should stay clear.
I think thats the general age for the restrictions of gambling although, in sone countries it's 21 and above. It's a good thing that they gave legal right to people that are +18, talking about depression and mental health issues, imagine If kids where allowed to gamble, a good percentage of them would had died from depression, cause they won't be able to control their emotions like the adults would, when they lose huge money to the house.
Also 18+ is a working age for most countries, and i think it would be bad for people below that age to be allowed to participate in gambling, cause lots of kids that could not afford the money or got source of income to fund their betting habbits could turn into steal funds from parents or others to gambling, which is not good to the society, it could promote high rate of theft and criminal activíties by those kids.
Lastly, i thnk you'r right when you mentioned that people with BP pressure issues shouldn’t be allowe to participate in gambling, so as not to endanger themselves when they lose funds, but the question is how would casino's figure out those people with such issues?