Hi Pat,
And let me also Welcome you to CycleFish!!!
Glad to hear you are taking up riding, and since you asked for advice I am assuming you are the kind to take it. I have to agree with just about everything above, and please don't assume we are all just picking on you for your "showing off" statement. I can almost guarantee you that 9 out of 10 of the people who responded (including myself) were just like you if they started riding as a teen or young adult. But years of riding experience and seeing a whole bunch of people getting hurt or killed has given us some wisdom to share with you to ensure your riding experience is a safe one.
Yeah, I can try to justify the stupid shit I did on bikes with the roads were less crowded back then, and the bikes today are much more powerful - and true as that may be, it was still just dumb stuff that shouldn't have been done by a new rider and I am lucky to be here today.
To me, and most everyone here, riding is one of the greatest experiences in the world, and I am sure you will feel the same when you start. I'm not going to tell you to go out and get a little scooter that you don't want just to learn to ride. Go out and get a bike you want and can be proud of... just be sure to do everything you can to limit the dangers that are inherant to motorcycling. Take a course, practice in areas where there are no cars, and ALWAYS ride within your limits. As you spend more time in the saddle, your limits will continually advance and you can fully enjoy riding!!!
Now to answer your original question... What should you look for in a used bike?
First of all use simple common sense as you would in any major purchase... make sure the individual you purchase from is someone you can trust.
Look for a bike that has been well kept. Typically if the owner took pride in their bike and kept the appearance up, they also took the time to maintain their bike.
Ask for service records or service history, Today's motorcycles when well kept will run for a long time. However a bike that has had the maintenance neglected will give you nothing but problems in its later years.
If possible take it to a local mechanic for a quick once over. You may want to call around in advance and find a local shop willing to do that.
You may also consider purchasing an extended warranty once you have purchased the bike. You can check with your local dealer on that, or there are a number of independent companies that offer them.
And most importantly - don't be in a hurry to get a bike and take something you are not 100% happy with or comfortable about the condition or price. There are more used bikes on the market today then I have ever seen - some great deals and some real dogs (no offense to my K-9 friends). Take you time and keep looking until you can go home without feeling like you compomised.
Again, Welcome and we hope you find a bike you love and have many years of positive riding experiences!