Can you correct your posture at any age?
Age is not a hindrance when it comes to correcting the posture provided you choose the right way.
Practicing yoga, different exercises, meditation, etc. are some methods to correct the posture. These methods will require your consistent efforts and wait for good results.
If rounded shoulders worry you, then you can use posture corrector brace to correct the posture. This is an easy way to get a correct posture.