I think a dirtbike is a great starting point but be very careful
will be great to learn basic mechanics of riding, throttle control, location of brakes, and getting comfortable using them.
Down side to a dirt bike and to go completely against what someone said already.
Keep this in mind, this and i have seen it 100 times!! There is no lip on the back of the seat to help keep you on the bike when it takes off and if you do not have at least one foot on a peg you are not truly on the bike. Scenario is you stand flat foot, give throttle, pop clutch, bike goes.....Oh you were standing never really on the bike so the bike goes and you stay behind, now the problem... you are still holding on to the throttle. Now you are hanging on giving the bike uncontrolled WOT with nothing to help you. At this point as a beginner you have to just let go and dump the bike cuz you will most likely never get back on the bike or get it undercontrol. If you have some experience, you can hold the clutch and ride out the speed but that is a bit much to ask from a terrified beginner with their life flashing before their eyes.
On that note, DO IT!! don't be stupid, a dirt bike is just as dangerous wear all the proper gear, helmet, boots, gloves, pants and some form of a jacket no matter how small the bike. And do it somewhere safe!!!, a large field is ideal, a large dirt parking lot can be fine as long as it is LARGE and no vehicles in it and or ledges, concrete walls. Do not under any circumstances try it on a street.... you will most likely hit a parked vehicle, and since the dirt bike is not licensed or insured you are EF'ed
I watched my good friend do just what i described on my wifes little KLX125 after 15 minutes of instruction, and going through practice scenarios where i specifically said, KEEP YOUR DAMN FEET ON THE PEGS!!
He was lucky, i made him suit up with gear, he escaped with much pain and soreness and some stitches but nothing life threatening. We tease him to this day about the day he wrecked my wifes dirtbike (my wife is like 5'4" 115 lol) insult to injury
Just my 2 cents
oh yeah, check out youtube vides of people wrecking dirtbikes and you will see exactly what i described.
cheers
Just found this one, this is prime example
http://www.youtube.com/watch?v=oWNEj...eature=related