Age Before Beauty by Tatsumaki_sama
Age Play by laylabinx
wherein it was discovered Steve had lied about his age when he entered the army and is still (at the time of the Avengers movie) a minor. They were both excellant and I would love to read more like these. I know it's not a common theme (the only others I recall reading were in The Sentinel and Stargate SG1 fandoms quite some time ago) but if anyone can turn up any (with any of the characters) I would very much appreciate it.