Younger maybe better physically having some life experience and strong mantality of someone a little older is also a good thing. If you believe you are ready and capable go for it. I'm on the older side, but mentally worlds stronger than I was when I was 18 my physical limits can be pushed by my mind, I may not recover as fast but mentally I am prepared for that. Think it over from different perspectives and if you feel you should go then do it. I think combat can affect younger people more than older, from what I have heard from the members of my family that have served. Even being able to separate your civil life and military life can be a task for some. Not all are the same and your training plays a big role in it. So pros and cons to consider.