I've been doing it for a year and was able to move a styrofoam cup after about 6 months. Now I need to start all over again though. But just to point out that time doesn't matter. Dedication, patience, information on the subject and practice does. Know more about TK. Do you know about micro-tk and macro-tk? Not many people know those 2 parts and mainly think it's all about macro-tk. Know how it is scientifically possible(optional). You don't NEED to know how it is scientifically possible. But for me it helped me way better. The brain works chemically and also creates EM waves. In TK all you're doing is amplifying those EM waves and create an electromagnetic connection between you and the object(being one with the object energetically). This alone is what Mark has been practicing for years and got really good at PK.
But it all depends on the person. Some people are naturally able to have a boost of their psychic abilities while some just needs to practice more.