Waivers are good for one year from the date they are completed. Exception: Waivers for 17 year old players will expire on their 18th birthday and a new waiver will need to be completed as an adult.
Congrats! Now you can do your own waiver. If you had one signed by a parent, it automatically expires on your 18th birthday and now you can do your own (but still try to get mom to do your wash!)