Age is Nothing but a Number or is it?

I wonder why Jonathan is so eager to join the war and become a soldier. There is nothing fun and entertaining about war. It is indeed serious business. As far as I am concerned he is only 13 years old. He's not a man yet so he shouldn't be involved in war duty. He needs to grow up first and enjoy his childhood while he has it. You only get to be a child once. Life isn't going anywhere anytime soon so why rush into the war so early. Jonathan's not nearly as experienced as the others or as strong. He confuses me when he thought "Go! Do it!" because death isn't a very fun thing. Apart from that, you also need to be tremendously ready to take on war, physically and mentally. He'd also have to wake up early for some hardcore training instead of playing in his backyard with friends all day. I know some people say age is nothing but a number, but in this case it is. A child going to war with a man is not fair and is frowned upon on my behalf. Perhaps some kids such as Jonathan, do not think like me which is why they believe in war, not childhood.