Why do old people feel the world revolves around them?

Im 18F and work in a pub/restaurant and I'm sick to death of entitled old people. We close for food at 8pm weeknights and multiple times in the past few weeks i have old couples coming in 10 minutes before the kitchen closes telling us we must seat them because they are already here.
The worst example was a group of 4 old people who had booked for 7:45 (the latest available time to book for) and arrived at 7:58, which is 13 minutes late already, then when i said I'm unsure if i can seat you because the kitchen closes in 2 minutes i was given 'well nobody told me that' (you booked the latest time possible) 'why would you shut so early' (because its a tuesday, not a friday or Saturday) 'well ive booked a table so you have to seat us'. I seated them and said that the order must go through quickly to which they took 10 mins to order and ORDERED 3 COURSES meaning my shift that was supposed to end at 9 ended after 10 oclock, with them being the only people in the restaurant for the majority of that time. They also proceeded to not tip anything which im not usually sour about that but when you already know that the kitchen closes 2 mins after you sit down like come on were all here waiting on you and only you, atleast be kind.

I find it very difficult that the generation that feels they are owed so much respect by the younger generation feel no obligation in any way to understand that we are people to. Even down to things as simple as old people never saying please or thank you to me as a waiter or recently i had a woman who ordered an ice cream and when i brought it out and placed it down she immediately said to me 'well you need to go and get me a spoon then dont you' which is exactly what i was going to do after i placed the plate down.

Just because im a waiter doesnt mean i deserve less respect than everyone else, im just trying to fund my life along side uni..