On a whole, I'm completely against kids with locks. Sure they're adorable. But that's not the issue. Kids under about 10 years old just don't have the cognitive ability to understand choices and decisions. Even when they say they "want" something, they don't necessarily understand it, nor have they given it any real thought. So succumbing to their unthought out request is almost mean and selfish.
But that said, you know your kid. At 8, they are getting close to that age where they can think for themselves an make cognitive decisions. If you think they are able to really understand what goes into having and growing locks, let them.
I would recommend that you sit down with them, one day, and explain what goes into it. How they will have to wash their hair regularly. How people will make fun of them at school, and on the street. How they won't look like yours for a long time. Kids see time passing differently than your or I do. Tell you that something will take a year gives you a real sense of the process. Kids, generally, don't understand how long a year really is. They haven't lived as many of them to get a real grasp of it.
Now, are you ready for it? Are you ready to have people look at you like you're a terrible parent? People staring at your locks and judging is one thing. You can shrug it off and say they don't know you. While you should be able to have the same reaction when they insult you for letting your kids hair go crazy, it can have a different emotional effect. People are no longer judging you for you. They are judging you for the care you give to another person.
So if you think your kid is ready, and you think you are ready, do it. But don't do it if it's just because you think it's cute that your kid want's locks.