It is generally not too late to purchase long term care insurance until you are in your late 70s or early 80s, depending on the insurance company's age limits. However, the premiums increase as you get older, so it is recommended to purchase the insurance earlier in life to lock in lower rates. Additionally, your health condition at the time of application may affect your eligibility and the cost of the insurance. It is crucial to consult with an insurance professional to determine the best time to purchase long term care insurance based on your specific circumstances.