> If you look young, how can you even buy alcohol or cigarettes (in my countries case even energy drinks) or get in a club?
It is possible to go your entire life without ever doing any of those things, or having any desire to. And as a general rule, it's the people who are of legal age who least care to do them. Also, some countries don't have age restrictions on such things to begin with (or don't enforce them at all).
> post office when receiving package
Who goes to the post office to receive a package? They come to you, and are then satisfied by the fact that they delivered the package to the address on the label.
> getting drivers licence
This a major reason why this is pointless. If you're going to have an ID, how do you identify yourself to get the ID? It's fully circular. You can't prove who you are unless you can already prove who you are, in which case you already have an ID.
In the US a large percentage of the population don't have passports. When you get a driver's license, they nominally ask you for some other ID, most of which (e.g. birth certificates or company/school IDs they have no way to authenticate) are trivially forged and useless at proving the person is who they say. Because it has to be that way -- you can't make having an ID a condition of getting an ID.
The whole idea is silly. Identity is context. If you create an email address with Google, you set a password. Then Google knows you're the person that email address belongs to because you're the one with the password. Your government "identity" has nothing to do with it, nor should it.
> opening bank account
The only reason banks care about this is that the government requires them to. Otherwise they would be completely satisfied to give you a numbered account with no person's name attached and simply put a hold on your deposits until after they've cleared, as they do for most anyone regardless.
> getting loans etc.
To get a loan what they care about is whether you're creditworthy, not what your name is. Prove that you have a job and a history of paying back debts, or post some collateral, that's what they want.
One system by which they automate this is to have credit reporting agencies that aggregate this information and associate it with your name, but there is no inherent reason it has to be done that way -- and some good reasons not to. See Equifax data breach.