In Season 3, when Ryan is with Sadie in the pool house, Seth finds the door locked when he tries to enter and states "when did this door ever have a lock." Ryan mentions he added it for privacy. In Season 1, when Hailey has the huge New Years party, she locks Ryan and Seth in the pool house, so they won't spoil her fun.
In Season 3, when Ryan was seeing Sadie and was unsure about asking Marisa to come to his birthday party, the calendar on the Cooper's wall had the number 19 circled as Ryan's birthday and the next day was indicated as the first day of Spring which would be in March. In the last season, Ryan is perusing a scrapbook put together by Taylor, which had included their hospital bracelets from when they both were in a coma. Ryan's bracelet showed the date 09-05-86.