They are all different. I have 5 puppies now. One's ears were up at 4 weeks (see Quints are Thriving in the Nursery Forum). They are 6 weeks old now and two have their ears up all the time, two are half/half and one has not come up yet, unless he is startled and then they come up alert.
Usually if there is a problem with them coming up on their own, you can just shave the top third triangle of the ear and they will come up. I have never had to tape any, but there are instructions for that here on YT.
By 16 weeks if they are not standing on their own and the shaving did not work, then I would look into taping them. I have noticed from being here on YT that some of the larger dogs have more floppy ears. I am not sure if that is genetics or if they were just not shaved or taped when younger.