Age has nothing to do with the matter. The minimum ages for drinking and smoking are legal matters - not medical facts. Most countries (even the USA) have no minimum drinking age - what they do have is a minimum purchase age. And buying alcohol or tobacco has no effect at all on a person's health; it is the use of these drugs that can cause problems.
And insofar as use is concerned; alcohol in moderation is very good for you; tobacco - in any quantity at all - is very bad for you. At any age at all.