Your goal should oviously be to run as fast as possible. However, I'm not sure if there really is a specific time that you must run in order to remain at OCS. I attended OCS this summer but was NPQ'd due to shin splints. Many of the candidates I encountered were running between 22-24 minutes and continued at OCS. However, my OSO said that 24 minutes was the threshhold and if you ran slower than 24 minutes they would send you home. Again, I'm not convinced that's an absolute either. A lot of what you will hear is designed to test your motivation and make you strive to meet ever increasing expectations.
The age waiver, as far as I know, isn't tied to a specific run time and my OSO never indicated the two were related. I received an age waiver due to my age, 31, and was running between 23-25 minutes. I too am looking to re-apply and continue to work on my run time. Keep in mind that an excellent run time (or overall PFT score) will make you look better even though you're older.
My advice it to stay motivated and run, run, run! My opinion is that OCS believes strongly your commitment to the process will make up for any physical limitations so long as those physical limitations don't prevent you from completing the process (e.g. shin splints, broken arm, concussion, etc.). Good luck!