If you have trouble reading the small text on your iOS device, you can enlarge it, at least in some helpful locations. To configure the size, go to Settings> General> Accessibility. What you'll want to change is (unsurprisingly) labeled Large Text.
Once you select that, you'll be given a bunch of different font sizes to choose from, so pick the one that blows your skirt up.
As I noted, this won't change all of the text everywhere, but for example, it will enlarge calendar event details:
Your list of contacts:
And text messages (both the list of them and each individual message):
It'll also affect the text size when you're viewing or composing an email and the size of the font in the Notes app.
I find larger iOS fonts so much easier to read, especially on my iPhone, and yet I must confess that I leave this setting off anyway. It's probably vanity. Don't be like me, kids.