To add my two cents to the underage drinking issue, because it raises some intereseting ideas as they relate to the Do Over story.
1) It is illegal to sell alcohol to minors because they are less physically able to handle the effects, and they lack full adult judgment-making - as a physiological matter - when it comes to making choices about risks. I do not mean to offend any of the younger posters on this board. But there is medical evidence that the human brain continues to develop throughout the teen years (and to a lesser extent beyond). The last part of the brain to develop is the prefrontal cortex, which is responsible for balancing risk, long-term planning, and the like.
The question is whether these two reasons dictate that Davey (and Sean) should be treated as minors for the purpose of alcohol consumption.
As Dan points out in the story, they are physically less able to handle the alcohol. But are they lacking in full adult decision-making brain processing capabilities?
This is an interesting question that I think Dan has glossed over in the entire series. We have been repeatedly told that Davey is stuck with the body of someone younger - for good and bad. His hormones are allowed to play some part in his behavior. However, Dan has never addessed how Davey's decision-making process, when it comes to issues like risk calculation or planning, might be affected by the fact that he does not have the developed prefrontal cortex of an adult.
So far, we are presented a fictitious world in which this is not addressed or demonstrated to be a problem. If you have suspended your disbelief thus far to think that Davey has the mental processing abilities to advise the United States government on serious issues of military strategy and politics, as he has done in different time lines, then you have to accept that Davey has the ability to assess, like any other adult, whether and how much he should be drinking.
2) The second interesting issue is what message you take from Do Over about different subjects, like time travel, religion (hi Snow Dog) or something like drinking alcohol.
I don't see how Do Over condones underage drinking or gives a suggestion to any minors that this is acceptable behavior. The story - with Davey's past, with Brian in DO and with Davey/Sean in DOR - clearly presents the effects and consequences of underage drinking and/or alcohol abuse. It doesn't glorify drinking in the least. I think it is better to have a series like Do Over address the situation of underage drinking and portray it in a negative light, which it does, than to pretend that this doesn't exist at all.
Oh, and EMoe, Wyle E. Coyote is my role model for how gravity works. It does not engage until you realize you are no longer on the cliff. And large objects falling on you only hurt temporarily. I don't know where I'd be without Looney Tunes...