"After all, if you don't get glasses, your vision will only worsen..."
I disagree. I think the truth is more like your eyesight will get worse if you get glasses. Your eye muscles will simply "give up" and give in to the magnification which will need to be increased over time as the muscles grow more slack from non-use.
I am nearly 53 years old and I don't wear glasses. It's true that it takes me a little time to focus in dim light but I feel that is a small price to pay. It's also true that because of the changed shape of the lens my eye muscles have to work harder and so I get some slight blurring when holding text up close (certainly 5-6 point text) and I can feel the muscles pulling very tight. If I wait a while though it clears when blinking. The way I see it, most text I have to read is 12 point and that's very easy for me now.
I have been doing convergence and divergence exercises for over 5 years and I also use traynor glasses, training each eye independently using very fine print at various distances. This works a treat for me and I thoroughly recommend it.
I haven't heard of any exercises that can limit it but this site can help you determine what kind of reading glass strength you might need http://www.readingglassworld.com/content/Eye_Chart.htm. After all, if you don't get glasses, your vision will only worsen