Age is just a number seems to be the mindset of Carrie Underwood's 4-year-old son Isaiah, who has a crush on country singer Maddie Marlow. Underwood revealed her lovestruck son's crush on Marlow via Twitter, UPI reports. "This morning my 4-year-old, who hates wearing jeans, asked to wear jeans so he could 'look cute for Maddie,'" she tweeted. "He also asked me to fix his hair and to get him some flowers that he could give to her. Don't you break his heart @MaddieMarlow!!!" Marlow responded that she "seriously could've cried" and congratulated Underwood and her husband Mike Fisher for raising the "sweetest" boy. Marlow is part of the duo Maddie & Tae, who just so happens to be opening for Underwood on her Cry Pretty 360 tour.