Well, not every place is Silicon Valley ci.
Regarding the original question, I see no reason why it wouldn't be normal if the parents aren't treating their adult offspring like children, and the adult offspring are contributing to the household.
My best friend, who is my age, around 56 or 57, has lived in the same home with his parents on and off his entire life.
He's always had a good job, but sometimes it just made more sense for all of them to live together.
Notice I didn't say "in his parents house"
In his late 30's/early 40's, his mother was going through her final illness, and it made more sense for him to be there for her.
Another time it saved on significant transportation costs until he found a house he wanted to buy, which took well over a year.
When he first graduated and started working, there was no reason for him to leave. They had a lovely home, I'm thinking they all owned it together. Why not? It didn't make him less of an adult.
Most recently, he decided to drop out of the rat race and moved to San Miguel, Mexico. He packed himself, his 3 dogs and his 93 year old father and off they went.
He's never lived his life any differently when he's living in the same home as his parents, as when he lives somewhere else. They don't live any differently either.