Special situation: I took a teen class but have since turned 18
Texas regulations stipulate that if you took a teen driver's ed course, you must complete all of the teen requirements before you are eligible to take your driving test (road test), even if you are now 18 or older. This means you must complete all 32 classroom hours of the teen course, have your 30 hour log completed (as well as the 7-hour in car instruction + 7 hour observation log, if you did parent taught), and watch the Impact Texas Teen Drivers video (as opposed to the one for adults). You will also need to provide a current verification of enrollment for your school, or show proof that you have graduated (diploma). See this page for a list of requirements based on whether you have taken a teen or adult driver's ed class.
The only way to get out of the extra teen requirements is to take a 6-hour adult driver's ed course, such as this one (choose "Texas Adult Drivers Ed"). Make sure to bring the ADE-1317 course completion certificate to DPS when you go for your driving test as proof that you have completed an adult class.
PLEASE NOTE: Your learner's permit expired when you turned 18, meaning you cannot legally drive on the roads (even with a parent or other driver 21 or older with you) without first renewing your permit. If you are ready to take your driving test, you can test at any DPS office even if your permit has expired (but you cannot test at a driving school unless you first renew your permit).