This happens to all (or most) parents with grown children, and it certainly has to us. The first time you have dinner earlier than usual, whatever that is, the teasing starts…”You’re onto the early-bird menu now”…”How old are you anyway?”…”Was this your idea or do you have old friends?”
We stubbornly resist the temptation to dine “earlier than usual” so when we’re cruising it’s not likely we’ll be in the dining room for an early seating. Lots of other cruisers like the idea, however, so much so that Princess Cruise Line is introducing a third, earlier seating.
It MUST be popular.
The other traditional dining options are at 6:00 and 8:15. On Princess Grand and Diamond class ships, the early-birders can eat at 5:30. 
On Coral class ships, plus the Sea Princess, they can go even earlier — 5:15. The new option is not available on the Ocean, Pacific or Royal Princesses, nor on any Australia itineraries.
Of course, Princess has “Anytime Dining” also available on most of its ships, so you can have a different meal and restaurant every night. Now that’s what we like.
At least…that’s what we tell our kids.