Sounds like a good idea to me. I'm in favor of synchronizing ALL the various ages milestones that apply to adulthood to a single age. Age to buy tobacco, alcohol, guns (long gun OR handgun), adult material, age of consent, age at which you can be tried as an adult, and draft age. These are all things that apply to adults, and we should have a fixed and common age for all of them. 18 sounds like a proper milestone for that.