When you email the note it should create PDF attachment in the email. You can not change the size of text in that PDF; however, if you increase the size of the text in OneNote before emailing the note it will create a PDF with larger text.
To increase the text in the note tap and hold on some text until you get the pop-up menu. Choose Select All (selects the current paragraph), then Select All again from the next pop-up menu (slects all text). Tap on the Font tool in the tool bar and choose a larter size.
The default font/size in OneNote appears to be Calibre 11. When I print this I get something slighly smaller than what you'd see in most printed letters, but I wouldn't call it all that small. When I change it to Calibre 20 it's about the same size as a children's book. You'll have to experiment to see what you can get.
I could not find a convinient way to print or copy notes out of OneNote beyond emailing them as PDFs; but I don't use OneNote, so there might be some hiden trick I didn't find.
Note: Having to chose Select All twice to actually select all text is pretty weired. OneNote is the only app I've seen that does this.