Wear a dastar when you are ready to carry its weight and recognize that your head is no longer yours, but it is Guru Sahibs. I am sick of people wearing dastars but still engaging in other stupid activities, it just brings shame to the name of Sikhi and Guru Sahib. I'm in no way saying you will do that, but make sure that when you take this step, it's from your heart and you have the desire to do it, otherwise it's just a false ritual (e.g. if you wear it to impress others or something). Dastar is extremely important in Sikhi - it's a symbol of our sovereignty and should be respected to the highest degree. I feel Gursikhs are slightly incomplete without a Dastar, so eventually, everyone should wear it or should at least have a joora on top of their head. But I also feel that whoever wears it should understand its significance and realize what they're representing.