Julz,
Ignore the idiots. Kids start riding as young as 4 with PW's and the like. Girls should ride as much as guys. My little sister rides and has fun. Riding is not a "man" only thing. if you want, some of the plastics manufacturers, like ACERBIS, make pink and purple replacement plastics for the KLX.
at 5'5" The KLX would be good. Make sure he gets the regular wheeled version. If there is a "tall" wheeled version, the bike may be a bit tall. Thus it wouldn't do much for your confidence since you can't touch the ground.
The other option is the TTR110E from Yamaha. Same type of four stroke 110CC motor in a small wheeled package. The TTR110L is the big wheeled bike.
See if your dad will take you to the bike shop to go sit on them. Realistically, you only need to have 1 foot on the ground to ride a motorcycle, just like a bicycle. However, having both feet touch, even if it's the balls of your feet will help your confidence when you're a beginner.
HTH,
D