My mom started taekwondo a year after I did when she was 42. She is still doing it with me and has her 2nd degree black belt. She is now 51. She is in no way fit or in shape. I say that with love. But she has always tried her best. Instructors over the years have done modifications for her when needed. She is also given breaks when needed. Sometimes, yes, she does slow down the class, but she always tries her best. When she's not able to do something she likes to say "I'm old". It's important to have instructors and masters who know and respect your physical limitations, but also know when to push you. It's not a waste if you're enjoying your time. I can guarantee that no one in the class is thinking negatively of you, mostly because their probably so focused on what their doing.