Judd Apatow, executive producer of HBO’s “Girls,” forgot his protégée Lena Dunham’s 27th birthday last week. “I found out from [my daughter] Maude, who saw it on ‘Entertainment Tonight,’ ” he admitted at the Waldorf-Astoria yesterday, where he accepted a Peabody for the show. “I got her no presents, just a late-in-the-day e-mail. I was not a good friend.” Apatow added, “I wasn’t invited to a party. Maybe there was a party, and I didn’t get to go?” Dunham was seen looking happy on the “Girls” set in New York on her birthday. Apatow, 45, known for his movies focusing on emotionally stunted men, including “Knocked Up” and “The 40-Year-Old Virgin,” told us he identifies with the struggles of the 20-something women on “Girls.” “I was broke, so I understand that — and I had a lot of weird jobs in my early days,” he said. “I washed dishes, waited tables and was a busboy. I dated all sorts of people that broke my heart for a long time before I found my beautiful wife [Leslie Mann] . . . And I’m very feminine, so I relate in that way, too. I’m emotional.”