Actually, I don't think the vision requirement is an age thing. I read an article a while back that said older astronauts may be preferable because older people seem to handle radiation exposure better than younger people do. I couldn't find the original article I read but you can find something similar here. This article says:
Those radiation limits vary with age and gender. For 30-year-old astronauts, the maximum allowable mission length for a female is set at 54 days and reaches 91 days for male spaceflyers, the report stated. By age 55, the total days in space max out at 159 days for female astronauts and 268 days for their male counterparts.