No, it's not too late. But what I would suggest is proper technique, otherwise you may strain something that your body is not used too. It may be better to have a yoga instructor help you with the technique without hurting yourself.
The first rule that I tell everyone: listen to your body, and approach your limits slowly. Yoga is not about how far you can twist your body into a pretzel, but rather accepting yourself for who you are, and then making improvements from there.
Yes, a teacher/structured class is a good idea, but select one carefully. There are dozens of styles and teachers are often certified with a minimum of training.
As for an instructor, just go to three or four different classes and find out. Classes are offered all over the place, from boutique studios, exercise gyms, even the YMCA. Some of the best teachers simply work out of their homes. If you are in the Atlanta area, pm me and we can talk.
Individual classes cost around $15 for a single drop in session, and will offer discounts for a series of sessions. Price of a class is not tied to the quality of the teacher. You can find an excellent instructor at your local community center - the class I am currently in is "Pay what you can" where you just drop money into a bowel by the door, and the teacher is invited accross the country to teach at yoga schools.
When you go to your first class, it is customary to remove your shoes and socks, and wear loose fitting clothing. You can bring your own mat ($15 at Target), or the facility will often have them, sometimes for an extra charge. There is no other sport where the cost of equipment is so low.
Show up 10 to 15 minutes early and introduce yourself - if the teacher does not ask you about your previous experience and/or if you have any medical conditions, then do not go back. If they try to push you past your limit, do not go back. If they are more interested in looking at the pretty girls....well you know the answer.