I think a lot of people forget how young Rapunzel is supposed to be. In the second act, when Rapunzel's already gone pretty crazy, the Witch asks her what's wrong and she says:
"Oh, nothing! You just locked me in a tower without company for fourteen years, then you blinded my Prince and banished me to a desert where I had little to eat, and again no company,and then bore twins! Because of the way you treated me, I'll never, never be happy!"
Fourteen years. Seeing as how the Witch took Rapunzel when she was a baby and kept her trapped that whole time, she can only be in her mid teens. Now, the idea of a teen bride is completely normal for the time (and Rapunzel was 16 in Tangled I believe), but that does change casting quite a bit. Emmy Rossum, just one who has been mentioned, looks younger than she is, but not like a teenager.
This also makes a 40 year old Baker a little tricky...if his mother was pregnant when he was "no more than a babe", he can only be max 6-7 years older than Rapunzel, who can't be older than 16 or 17. I don't know if most people would notice this, but I thought of it yesterday while I was watching the OBC. It is something to consider with casting, as it makes the overall age of all the characters much younger.
Give me a bottle of bourbon and half a chicken and I'll conquer the world!