There's lots of ways to increase or zoom "most" but not all font sizes that appear in different apps & on the web. I'm fortunate to have 20/20 vision, I work for hours on my 13" MBA no problem.
Overall it's such a nice laptop I'd encourage you to remember there's a return period which facilitates your ability to try one. Apple has in my opinion the finest customer service & ease of returns of any company.
Buy one & try it. There's a good chance that within a few days of usage you'll adjust & really enjoy it.