Is this a generation thing or a personality thing?

I think it is a personal thing. There have always been people who are casual and unreliable. I had an uncle (born 1910) who was generally known as the 'the late Mr Smith' because he never turned up on time for anything. My deceased sister was another known for her erratic arrival for anything.

I think it is a personal thing not generational. I have a friend who will make arrangements months in advance and then at the last minute make a lame excuse. I have another who likes to be so organised she picks everyone up for a lunch out, so she knows we are on time.
My DDs fall into both camps, one with their friends who seem to be more casual and more formal with me and their father who is a stickler for keeping to arrangments and time. Can't say the same for his family after sitting until 3.45 p.m. waiting for his DB for lunch we tucked in and were just finishing as they came down the drive, they had "Slept in" believe if you will.

I know what you mean .
I far prefer to be organised when going out .
I have friends who want to out -then get into some sort of panic over it and change their minds .

And others , who are so casual -that they are never ready on time so that actually going is totally chaotic .

Definitely a personality thing, I think. I cannot abide unpunctuality. I would rather be an hour early for something than five minutes late. I like to plan things in advance and if I am let down at the last minute, do not for one minute think I will forget that.

When working I found planning things in advance meant spending much longer on the task, and subsequently tweaking it. If I left it until later, I'd use an adrenaline rush to get it sorted quickly.

It depends who the friend is. If someone has come some distance, or its very special, then it's every effort. but as I have off days and some friends do, we have arrangements that are, "if needed, postpone same day, no hard feelings". So there may be disappointment, but not take it personally if those need to be altered.

But thinking aloud all these occasions have been remembered, and people know where they are.

No, I think it's a personality rather than a generational thing.

My DC are very well organised and have to be.

Since I retired I tend to be more of a last-minute person in organising outings, trips, holidays etc. although I used to be very organised (is that generational or just that my time's generally my own now?).
But I would not let anyone down unless it was absolutely necessary.

My children are well organised and keep me informed if there’s any changes as far in advance as is possible. 2 DGD is a very last minute person but she doesn’t drop out. I had one friend who was well known in our group for ‘forgetting’. I used to ring and remind her but eventually decided it wasn’t worth the effort.

Yes, my children are more difficult to pin down than I am, probably because their lives are busier and they have more options, but when they've agreed to do something they keep to their word.

Personality thing in my opinion, I make and stick to appointments and arrangements and so do my children.

I can deal with no plans - it's the pulling out/cancellation that I struggle with.

crazyH

Generational, I think.
I hate leaving things to the last minute. On Sunday, daughter and I went to Birmingham for a show. On Saturday, early evening, I texted her to check on pick-up time.( she was going to drive). No reply. I didn’t want to keep ringing or texting , because she works and would probably be tired. I left it to her. No call, no text, until 8 a.m. Sunday. ‘Will pick you up in 15 minutes’. Glad I was ready ?

Your daughter and I would be a perfect fit. She may be too young to be my child, but I like the "no plans" method.

Generational, I think.
I hate leaving things to the last minute. On Sunday, daughter and I went to Birmingham for a show. On Saturday, early evening, I texted her to check on pick-up time.( she was going to drive). No reply. I didn’t want to keep ringing or texting , because she works and would probably be tired. I left it to her. No call, no text, until 8 a.m. Sunday. ‘Will pick you up in 15 minutes’. Glad I was ready ?

I think it's a personality thing, as many people of may age (63) have what I see as a cavalier attitude to arrangements. If they don't feel like doing something they cry off at the last minute, are late without good reason, and generally let people down.
I really don't like it, and have stopped bothering with friends if they do it too often.

I know what life happens, and it's not possible to keep to every arrangement you make, but IMO crying off without good reason is saying that your time/needs are more important than those of the person who may have refused another invitation or gone to other trouble to keep the one with you.

I do think that the ability to text excuses has made things worse, but I don't think that young people are the worst offenders - far from it.

I also tend to leave many things last minute, give myself a very narrow margin of time. That's personality, my opinion. I don't like plans at age 77.

I also find them a bit blase’ about social arrangements. For example, DIL made arrangements months ago to meet two friends for a birthday celebration weekend in Las Vegas (we live in CA about three hours away.) At the last minute she pulled out because she didn’t feel like risking exposure to COVID in a place she actually doesn’t really enjoy anyway. She took and sent a photo of a friend’s positive COVID test and said that it was DS’s and that’s why she couldn’t come.

The above isn't acceptable, to me, no need to be a liar, I'd rather admit why going is never going to happen.