My eyes are terrible, somewhere in the neighborhood of 20/80 but with glasses or contacts they're fine (20/20) for the most part. I don't really know other than that what constitutes good eyesight for shooting or what else can go wrong with my eyes but anybody with glasses knows you don't know what your missing until its fixed.
I'm nearsighted, and I shoot irons. I did have to give up on the open sights, which is why I recommended the Tech Sights. I couldn't make my eyes focus on the front sight any more with open sights. My eyes would involuntarily shift focus from the front sight to the rear sight, and there wasn't a damn thing I could do to control it. A military style aperture makes a world of difference, because it basically eliminates the rear sight plane from your field of focus.
A lot of folks will say start with optics because they think you will be a poor shooter at first and optics will make it easier, and you'll have more fun, and this that and the other. Then later, I suppose when you get serious about learning marksmanship, you should graduate to irons? Frankly, although I respect their opinion 100%, and I do believe there is some validity to it in some respects, I think like Leaky Waders said, if you are printing 2" groups with the stock sights on that Marlin at 50 yds, you are not a bad shot, and you can definitely improve that group with some better irons. If you just want some glass, that's one thing, but if you are really trying to learn marksmanship, I think you are on the right track shooting that .22, and your next purchase should be some good sights. You're young and your eyes will only get worse as you age. You have the rest of your life to shoot with a scope. JMHO, YMMV, etc., etc.
That being said, you can certainly still learn and become an excellent marksman using a scope, but I believe in driving the standard before the automatic.
Jason