There's an article where De Niro talks about how they're possibly going to use some Benjamin button type technology on him as well as the other cast mates so they look younger. Him and Scorsese are very adamant about it happening and De Niro said in that same interview that they should start filming sometime next year. Like the quote above says, it seems like it's just about scheduling at the moment but it'll get resolved soon from what De Niro and Scorsese have said.