Tlouis:
That all depends on you and how you run your biz. I like to think everyone has a chance to do what they love - in fact thats my premise for business: Do what you love and the rest will follow (I also think thats a title of a book as well!). Passion makes for greatness. But not without vision and a structure to move it forward. Be sure to have a very defined idea of what it is you want to do (the statement in your post is adequate: I was thinking of opening a dojo and conducting classes part time-3 evenings and weekends. ages 14 and up- no kids. Based on traditional TKD and a lot of Hocks stuff as part of the training.
After this initial desire, get the opinion of those whom you respect and know want to see you succeed and ask them if you can teach well. If they give you the thumbs up then go for it, otherwise you may want to try something different. The desire to teach is a far cry from the ability to teach. If need be, educate yourself on this then try to swing it, otherwise you may wish to just do it as a hobby.
Also, don't take money out for yourself UNTIL you pay your bills, this is a great killer of businesses. As you say, you gotta pay the bills first. Keep your expenses low by having your students buy their own equipment up front. Setup a paypal account so you can take credit and debit cards as well as cash and check (contact MLEONE for that).
Have a liability waiver, t-shirts (so you advertise your classes), set class times that are convenient for most, a managable curriculum that is appealing and attainable as well as exciting and practical. Follow the guidelines that Hock posted they are golden and you should be on your way.
Good luck!