Since forever. Aspies have a hard time identifying their emotions. That does not mean they do not have them. I have a son with Asperger's. He has a knowledge of every emotions and sometimes it doesn't show to everyone. To me, he shows.
He understand when I am sad, he says he loves me, is physically affectionate with me and loves our pets and family. He just needs help to express it.
http://www.psychologytoday.com/blog/aspergers-diary/200809/asperger-emotions-and-adult-relationships