Can I encourage my friend to join the military?
Why do you want your friend to join the military?
He needs the structure in his life.
You shouldn't question what your friend wants to do with their life. Joining the military is a big enough risk and responsibility that they might regret it.
I want my friend to exercise more. It's not healthy for them to spend all day playing video games and being lazy. They need to go off the couch and join the military. People need to be more active. My friend will thank me for it.
Well if you think it is a great idea lead by example. Not everyone can do the job so it is wrong for you to even suggest. If he is overweight why don't you set up fun activities like hiking or bike rides?