Some things that can afflict a younger person do not show up so much in older persons; such as, suicide attempts, DUI's, suspended drivers licenses, some mental disorders, and type 1 diabetes, to name a few.
While under the age of adulthood, some of these conditions can make it difficult for a child or teenager to get approved for life insurance coverage, although there are usually life insurance policies to be had for each of these issues after a child reaches age 19. And sometimes more years of control or stability can actually bring the rate down for life insurance.
However, in the absence of those situations, it is usually cheaper to buy life insurance when you are younger, since rates are in part based on life expectancy, and the younger you are the longer you are expected to live compared to someone who is older.
Here's how you can compare life insurance prices for young people online with no obligation to buy.