After 15 years of leasing cars, I have decided to buy a used 2014 ES350. I plan on keeping this car for a while. Is there a product I can use to keep the headlights from turning yellow?

 

You have lots of options here.
Any parts shop have that chemical that you can buff up yourself. Some oil change places like Grease Monkey will do it for about $50.00 or Lexus dealer for $100.00.

Personally, I've tried myself a few years ago and then gave up.

 

I have an 2007 ES 350 with almost 100K miles and my headlight lenses look almost new with a kit I got from an auto parts store. Wasn't too hard of a job, just make sure you tape off the painted areas real well! The chemical products aren't up to the job if the car is over a few years old. A lot of the car wash people offer a service to do this.

 

The people installing our clear bra also installed the film over the headlights. The claimed it not only protected against the usual flying debris, but claimed the film is also "UV stabilized" and will prevent the yellowing from occurring. Cannot validate that claim, but our last 5 year old Prius headlights looked just as good after 5 years as new - but our cars are also kept in a garage when not at work or out and about on a weekend so the benefit may vary depending on sun exposure, if the claim is even accurate.

 

Get the X-pel headlight protective film. I've used it on a number of cars with outstanding results. Ten years on one car, the film and headlights are in perfect condition. Another car similar age, no X-pel, was polished several times, had to replace the headlights due to hazing/yellowing.