The lack of stress in my therapist was what first turned on the :idea: in my head that wondered, "how can I be like that, too?" After all, I was seeing her to help reduce the job-related stress that was making my hair fall out in chunks and my heart jump out of my chest!
I agree with the others, it's who you work for/with and getting yourself off the ground that are the stressful parts. But once the door closes and you're with your client, no matter how wretched the day is going, it all falls away and your focus is only on the person and the work ahead. You just CAN'T be stressed or negative and give a great massage, so you MUST to let it go.
As far as past injuries, there are so many, many different techniques and methods to help the body to heal, and some are more physically challenging than others, that there's no reason that should stop you if you're called to this work. If doing spot-treatment deep tissue all day is too much for your body, shift your desire to help others into a more gentle modality for your body, such as energy work. There are so many things to learn that you can live many lifetimes and not learn it all.
The inability to get bored with it is a big part of what keeps it fresh and exciting for us. Each day brings different people with different likes & dislikes, needs, hurts, and expectations to our tables. How can't anyone love that?