There is also the “I remember when <fill in the blank>” regret. Don’t define yourself by what you can’t do; focus on things you can do and do them well, and don’t regret the things you can’t. I remember when I use to do jodan mawashi geri without much effort, so they are a bit lower now and I’m a bit slower; does it really matter to the spirit of my training? If my answer was “yes”, then I should be examining why I am training. You may never be able to do some aspects of training as easily as others, or like “you use to”, does it really matter to the spirit in which you train?
Of course this can become a double-edged sword if you let it, inasmuch, there is a fine line between not physically being able to do something and giving up because it’s too hard. Only you can decide which it is.
Regret is a waste of energy as you cannot build upon it. Build on the dreams and make them realistic and achievable.