Is it acceptable to drink alcohol in front of senior staff during semi-official occasions? I am a graduate student, and because of the department's projects, partnerships with other institutions, and conferences, I am often out of office with the senior staff (supervisor, department head, other senior researchers and management, etc.).

After the work (e.g. meetings, presentations), it is often the case to attend social events (e.g. conference dinner or reception), or simply spend the free time with my colleagues (e.g. dinner in a hotel or somewhere out). During such events, which I consider also as partially work but not that official, people drink alcoholic beverages. Since I am often the only graduate student and the youngest person in the group (and usually the difference to the next person in age is >15 years), I am worried that in my case it might not be acceptable to drink and that it may project a bad image about myself. So I am wondering whether to always abstain in such occasions.

Of course this is not about getting drunk, it is about a glass of wine or two along a meal.

This also includes flights. When flying I always have a beer or glass of wine to fall asleep easily and to mitigate my fear of flying, but sometimes I am seated close to my supervisor or colleague.

I am not sure about the customs in academia, so I am asking: is it acceptable to drink alcoholic beverages in front of senior staff? (Again, to a limited extent.)

I could have asked in the Workplace SE, but I think that academia has a different etiquette.
Putting ice in good whiskey is universally unacceptable, but I think the answer may depend on which country you are in. If you are 20 in the USA, then no. Otherwise, you are an adult and you decide.