How do you know if someone drinks too much?

Context: my dad drinks a bottle of wine (or more) and at least 1 gin and tonic every night and has done for my whole life, He never gets “drunk” as in he is slurring his words, gets angry etc but even when he goes out drinking until 2am you can’t tell he is drunk. Ive never thought much of it since it was just normal to me but when i casually mention it to my friends they were shocked.
I am more just worried if it is bad for his health because he already is on high blood pressure medication but I don’t get told much else.