Rooney, Rodwell, Vaughan, Cheebs and Baxter all played at 17, which Ledson will be next year, Ross would have played earlier if he hadn't broke his leg as well. If the talent is there then age shouldn't be a barrier unless the player isn't physically up-to it, like Ossie, it took him longer to break through due to his size. Some smaller players have broken through at a young age but they usually have blistering pace to compensate like Owen across the park. I do think Lundstram will get a chance first though but it's Roberto's job to make that decision obviously.