44. Past the age of 40, vision tends to decline at a steady pace. mine certainly has. Us old people can’t really deal with font sizes much below 14pt- which tends to look large and goofy to younger folk. whatever size you choose or however you set up your grid, please gracefully permit users to override your choice, and ideally design and code your thing to not break when this is done. this isn’t just politeness, it’s the law in USA, the UK and Australia, along with the rest of WCAG 2.0
I mean, if you set your website at 10px you’re just invoking the wrath of Stella Young’s ghost. watch your toes.