Most insurers use the age of a traveller at the date of purchase, not the date of departure to determine the cost of insurance. This means that you could purchase a policy up until the day before your birthday and be quoted at a lower rate. It is also advisable to purchase your policy as soon as you book your trip. You will be covered from when you purchase the policy so if you need to cancel before your departure you will be covered.
If you have pre-existing medical conditions which you are sure will not cause any problems during your travel, choosing to exclude cover for that specific condition or to travel with limited cover will save you money on your travel insurance.
If your credit card offers free travel insurance, we highly recommend that you check to ensure that this insurance meets your needs by calling up your provider. To be eligible, most credit card companies require that a particular amount of travel or the return air tickets are purchased with the card. Check if you need to do anything to activate your insurance and ensure that your age and pre-existing conditions are covered.