There is no upper age limit. People in their forties, fifties, sixties, and beyond train Muay Thai successfully, and many start later in life specifically because the cardio and discipline appeal more than other forms of exercise. Children as young as five or six can begin in dedicated kids classes, which focus on coordination, fundamentals, and games rather than contact. Real sparring should not begin in childhood. In Thailand, children professionally compete young, but this is a culturally specific tradition that medical professionals increasingly question on neurological grounds. For most contexts, an age-appropriate progression looks like: ages 5-12 fundamentals and games, 13-16 light technical sparring, 17 onward unrestricted training. For older adults, the only real consideration is recovery — your body takes longer to repair than it did at twenty-five, so sleep, nutrition, and rest days matter more, and you should listen carefully to early signs of overtraining or injury. Start, scale to your level, and ignore anyone who tells you it is too late.