Philanthropist David Rockefeller is celebrating his 90th birthday by donating $100 million to the Manhattan university founded by his grandfather, the Standard Oil Co. magnate. Rockefeller, whose birthday is Sunday, is listed by Forbes magazine as one of the 100 wealthiest Americans, with an estimated $2.5 billion. “Now that I am getting to be 90, I thought it was time to take stock of my past and present,” Rockefeller told The Associated Press on Thursday. “It was time to provide more funds to these institutions that I have been involved in since I was a child.” Rockefeller University received its gift Wednesday. In April, the philanthropist donated $100 million to the Museum of Modern Art, which Rockefeller’s mother helped found. Rockefeller said that with opportunity comes responsibility, something his grandfather and parents instilled in him. Rockefeller, who retired nearly 25 years ago as chairman of Chase Manhattan Bank, said he plans gifts for Harvard University, where he studied as an undergraduate, and the Maine Coast Heritage Trust, which was created by his late wife.