Holy moly I'm outta shape.

[njdoxie]

Extremely flat looking, like you naturally have when younger

 

[Matt W.]

307 -- What about pushups? Back seems pretty straight if you do them right, yeah?

 

[307]

Push ups are a great option.

For a flatter stomach, reduced body fat is likely the limiting factor. Find a nutrition program you can live with and stick with it for a long time.

Exercise wise, plank variations, front squats, deadlifts all build trunk strength or endurance in a spine neutral position.