Here's a point that gets forgotten in a lot of discussions of this issue:
> We’re also underlining that our events are for over-18s, maybe even over-21s, by holding them in licensed premises. Most of us know students or even those who are working professionally in our field long before they are “adult.” Should they be excluded?
Depends.
Many conference I attended are professional, expensive and don't offer any alternative resources or attractions for younger participants. There are exceptions like some of the Python conferences and Maker Fairs but I doubt there would be many minors into a SQL DBA or serious embedded electronics event. Plus there is a liability issue to be considered when you mix immature adults with minors and blend in alcohol.
Under-18s can still enter licensed premises. At least here in the UK they can. And they often do, if my local that is more "5-year-old's playground" than "pub" is representative.
That's usually not the case in the US. It depends on the jurisdiction, but bars can oftentimes be fined for underage drinking if a minor is on the premises, even if he/she isn't actually drinking.
Even in situations in which the venues have discretion (eg, nightclubs, comedy clubs), venues often don't allow underage patrons to enter, because they know they're going to make no money off of them, and they're just taking up space that could instead be going to a paying customer.
Interesting, I wasn't aware that this was permitted in the UK.
Here in the US, under-18's often aren't allowed on the premises of a drinking establishment at all, so the OP does raise a point depending on the location of the conference.
> We’re also underlining that our events are for over-18s, maybe even over-21s, by holding them in licensed premises. Most of us know students or even those who are working professionally in our field long before they are “adult.” Should they be excluded?