I'm 20 too and always read articles with 300%-500% zooming if there is no vertical scrollbar. Occassionally putting the glasses down and still be able to read is a huge relief!
In 15-20 years, I will zoom as required. The issue really is less the font size and more the way the text stretches to the window, so if you zoom out then the sentences become far too long. I ended up having to alter my browser window size.
Edit: Just checked, definitely just the stretching, though a bit smaller would be better for me.
Tangentially related: Smashing Magazine recently did an outstanding article on readable web typography. (See http://www.smashingmagazine.com/2012/05/02/applying-macrotyp...). They say 8-12 words per line is ideal, though their example exercise seems to average closer to 15.
