It will depend upon your state laws as to what penalties you will be facing for driving alone on a motorcycle with only your permit. In some states it will be handled the same as if you were driving without a license which usually means fines and a possible suspension of your permit or provisional license.

You may also be required to attend a driver improvement plan and or have to keep your graduated license for a longer period of time before obtaining a license.

For example in Oregon their Department of Motor Vehicles notes that if you do not follow the rules for a permit or provisional license you could get a ticket, pay fines, your insurance rates can go up or your license could be suspended.

The DMV states in fact that you could be cited by law enforcement for violation of restrictions on a provisional license, which is a Class B traffic infraction. Convictions for violating license restrictions are used in the Provisional Driver Improvement Program, along with other traffic convictions. If you have either:

Two convictions, or
Two accidents, or
A combination of one conviction and one accident,

DMV will restrict your driving privileges for three months (90 days) to drive only to and from work or when required for your job with no passengers (except your parent, stepparent, or guardian).

These restrictions are in addition to the restrictions placed on a driver in the first year of a provisional license. A conviction for violation of these restrictions could result in a suspension or revocation of your driving privileges

If you get another conviction or accident, DMV will suspend your driving privileges for six months, even if you turn 18 years of age during the suspension period.

To find out what the penalties will be in your state for driving against the conditions and restrictions on your driving permit for a motorcycle, whether you are over or under 18, contact your local Department of Motor Vehicles.