Thank you for your question and photographs. I do not see that you have developed any marionette lines, and it is likely that you will have many years to go before you do. At your age it is important to start in the habit of a good daily skin care regimen to strengthen and protect your skin. This would involve the use of retinols and sunblock. Good skin habits now will pay dividends for years to come. Hope this helps
If the concern is downturning of the corners of the lips, injecting the DAO muscles with improve that. In addition, placing fillers for support of this area can be even better.
Just to start off, I want to tell you that no one in this world is symmetric. I don't think from your pictures that you have marionette lines. If you sleep on your side or on your face at night, I would consider sleeping on your back so you don't start to develop the asymmetrical wrinkles some people get by laying on one side of their face as they sleep.
It does not appear from your photos that you have marionette lines. You are likely not to develop them for quite some time.
EVERYONE will eventually have marionette lines, it's a natural part of life. Your pictures do NOT show any marionette lines, so you don't have to worry about anything at this point. Your lips look perfectly normal. Once they develop, they are easily treated with fillers like Juvederm.
Juvederm is a great product for injecting the marionette lines. There may be a tiny bit of asymmetry but you don't look ready for the injections yet. Use sunscreen and retinoids to prevent future aging. For now I would not get any injections.