You will do fine as long as it's something you want to achieve.
I ship off to basic in September 4, I to am 18 turning 19 in august 21. I'm about 5'10 and weight 175pounds...not fat but not skinny either.
Basic Training is a different experience for everyone, and you will have your doubts before you sign up, How can i prove it? Well for one i had it 5months ago when i was about to sign up, that and well everyone that i've made friends with in the future soldier program all had their moments, specially as the date is only less than 20 days away...I'm nervous but at the same time i feel excited...I hope you signed up by the time you read this post, since you did make it about a month ago...
42RM isn't trying to scare you by the way, he is giving you advice but from his own opinion, like i said everyone has different experiences in basic, i know friends who are now in Ait, who would love to go back to basic...others who are glad is over....
Everyone is entitled to their own opinion and advice, but you should only make your decision on this : Do you like the military life?
Good luck and if you did enlist good luck in basic and try to enjoy it, as i will try to do so as well