Most of what I would add has been said. I would reiterate that you can drink, and even if you drink more than you "should" - and, especially after this birthday, that's a goal that only you can set for yourself - most people, including those of us with diabetes, have done that at one time or another and lived to tell about it.
I do want to stress that, in learning how alcohol affects your body, the most important thing is not to become impaired to a point where you can't manage your blood sugar. For that reason, I would say pace yourself to begin with until you know how much you can handle, but as long as you're conscious and functioning you can deal with highs or lows. Obviously, lows are a more immediate concern, so especially upfront and if there's any doubt, err higher. Once you know more about how you react to alcohol, you'll have plenty of time in your life to figure out ways to mitigate the highs when you're drinking.
Also, if you're not aware, glucagon doesn't work when you've been drinking. It works by triggering the liver to release glucose, but if the liver is metabolizing alcohol, it won't respond to the glucagon soon enough in an emergency. Obviously, glucagon is an extreme measure under any circumstances (but it's not even the last resort...if you were unconscious, 911 could be called and the paramedics could inject glucose directly into a vein) but just FYI. Best to test often before it gets to that point, and if you feel like you're having any trouble staying awake, drink some water and take a break.
One last thing...it goes without saying that alcohol impairs judgment, but if you don't have much experience with it, it might not strike you that that also applies to your judgment about how much alcohol you want to be drinking. It might be helpful to keep that in mind, so if you find yourself thinking, say, "Oh, I've only had X number of drinks, I can have one more..." don't trust your judgment as instinctively as you otherwise might without analyzing that thought further.