@Joneszy said:

Why is Guinan in 2024 younger than she was in 1900 when Star Trek TNG went to Earth around that time?

Guinan revealed that she, an El-Aurian, has the ability to alter her own aging process to better blend in with humans.

Guinan should have realized she'd known Picard. She knew during TNG that things had changed in the timeline especially since Tasha Yar was there.

This is an alternate time line, when she never met Picard before. She might sense that something is wrong, but doesn't yet understand exactly what is happening. Later she will.

So she chose to be the same age during Mark Twain's time as she was as the caretaker of Ten Forward but years younger in The Picard. Didn't take her too long to know the Enterprise wasn't a war ship and she had never met Tasha Yar. Picard's group has knowledge of their alternate timeline yet didn't encounter any counterparts. I think it's just them making changes as they want them. Just as Klingons in Kirk's time were different than Worf but Klingons of Archer's time looked the same as Worf but Archer's time was before Kirk's and Worf's was after Kirk's.

@Joneszy said:

Why is Guinan in 2024 younger than she was in 1900 when Star Trek TNG went to Earth around that time? Guinan should have realized she'd known Picard. She knew during TNG that things had changed in the timeline especially since Tasha Yar was there.

I let you in on a little secret 🤫 Because the writers don't know how to write good stories of their own which is why they borrow from material which they haven't actually watched.