As pointed out above, there are exemptions from age discrimination. These are based on an identified need, or to comply with any applicable laws.
Offering discounts to pensioners or students, or families with children will likely fall within the 'identified need' category (that is, lower income). Other age discrimination, such as refusing entry to a venue, may also be legal if alcohol is served and the person is under 18.
Offering luxury lounge facilities doesnt appear, at first instance, to meet any of the categories to apply for an exemption.
Here we have a case where two people buy the exact same product. This could be at the same time, for the same price, with all the same terms and conditions. However one person is offered a free lounge pass and the other is not. The reason the second person is refused the lounge pass is solely because of their age.