Absolutely not! It is true that the longer you have your locks the harder it is to remove them without shaving your head (or cutting your hair very short), but it can be done at any point in the lifespan of your locks. All that you need is time, patience, some deep conditioner (I like to use straight olive oll), and a good, sturdy comb! The help of a friend or two would probably be helpful, too.
For more info check out the page on Dreadlock Removal!