Jessica and Ashlee's pop Joe Simpson has seen his share of highs and lows with respect to his highly publicized family -- and Joe is bursting with excitement at the prospect of becoming a grandfather.

"I'm too young!" Simpson joked to OK! magazine. "I'm very happy -- I can't be more excited." Joe adds, "Ashlee looks beautiful and is really excited."

The 24-year-old singer announced in May that she and hubby Pete Wentz were expecting their first child. Simpson and her Fall Out Boy recently celebrated the impending arrival of their little one with a Winnie-the-Pooh baby shower.

Joe managed his girls through the ups and downs of fame -- and has a piece of advice for the parents-to-be. "Hold on for dear life -- because it's a ride."