At 20 years, every active duty service member can retire with 50% of their highest three years of pay for the rest of their life. They also get evaluated for disability, and get that for the rest of their life. After 20 years, each year served adds 2.5% to their pension, so at 30 years, they would get 75%.
How much that pension adds up to depends on how high you moved up in the ranks. A 20 year enlisted servicemember will make a lot less that an officer. More senior enlisted will make a fair amount more than more junior enlisted.
Disability pay is based on how big of a mess you are physically and mentally, each disability pay band is the same, regardless of rank.
I didn't see anyone recommend in the comments, but I very much enjoyed Dreamscaper. It has a nice story revolving around the main character confronting hwr psychological issues in the world of her dreams. Combat is fun, slower paced and a little more tactical than most.
Also, fwiw, I'm not generally a roguelike fan, but I liked this one. Whether that makes you more or less likely to take my recommendation is up to you lol.