updated 11/07/2008 AT 7:00 AM ET
•originally published 11/07/2008 AT 11:50 AM ET
Ashlee Simpson may be only 24 – but, says her dad, she became a full-fledged grown-up the moment she learned she was expecting.
“The day she found out she was pregnant, she became a woman,” Joe Simpson tells PEOPLE.
“She’s concerned about what she eats and how she prepares for the child and [details like], is the baby’s room ‘green’ enough?” he explains. “It’s a transformation you never expect as a parent – you pray for it, but never expect it. She’s ready for this baby!”
And, Simpson says, his son-in-law Pete Wentz is equally prepared for their impending due date.
“Pete is the king of details, so he wants to make sure the baby’s room is just right – the right colors, the right sheets, the right look,” Simpson gushes. “He’s a great parent.”
“Papa Joe” (as he hopes to be called) also says that his eldest daughter Jessica is eager to assume the mantle of doting auntie.
In fact, Simpson – who manages the careers of both his daughters – says he’s doing everything he can to keep Jessica from bailing on her ongoing country-music tour.
“I’m trying to keep her out there until the baby’s born,” he adds. “I have a couple of other dates I need her to play!”
In fact, the only Simpson who isn’t completely ready for the new arrival is Joe himself. “I am too young to be a grandpa!” the 50-year-old declares. “But I am excited.”
As for the name of the Simpson-Wentz baby, the former preacher is keeping mum. “I’m not allowed to give any hints,” he insists. “I can tell you it’s not Joe. I wished, I tried, but it didn’t work.”