Re: out of shape
Go for it.
Be respectful of your body's need for rest and liquids--especially in summer. If you aren't used to working out, it's easy to let yourself become dehydrated and this is very bad for you.
I spent a *lot* of my first year sitting on the mat panting while other people trained, but they put up with me, and things slowly improved. (I still pant a lot. I need to kick my fitness up one more notch or I'm never going to make it through my next test. But that's a nice motivating goal for me to work on.)