How long should I train for a half marathon, considering various factors such as my current fitness level, running experience, and personal goals? Is it prudent to undertake a training regimen that spans several weeks or even months? What specific duration would be optimal for someone who is relatively new to running, as opposed to a seasoned athlete seeking to improve their time? Should I factor in any cross-training activities, and how might they influence the overall timeline? Furthermore, what milestones should I be aiming to achieve throughout the training process? Should I incorporate rest days, and if so, how do they fit into the overall schedule? How can I ensure that my training plan is both effective and adaptable to any unforeseen circumstances, such as injury or work commitments? Ultimately, what are the most critical elements that dictate the length of time one should devote to preparing for this exhilarating distance of thirteen point one miles?