Ultimately only him can decide for himself. If he tries to stop for you, it will not work. Your dad might suspect that you could be right, but at 50 it's hard to change your opinions or your habits. Don't pressure him. Don't count how many he smokes or ask if he smoked today, how many times this week, when was the last time he didn't etc.. If you push him he will resent you. Instead emphasize why you worry about his health, how you love him and make it clear that you love him no matter what and you support him. You can only help him with what he decides, you cannot decide for him. —
Manuki 1 min ago