Vyvanse is a central nervous system stimulant medication indicated for the treatment of attention deficit-hyperactivity disorder (ADHD) and moderate to severe binge eating disorder (BED). As you correctly stated, the drug name is lisdexamfetamine dimesylate, but there is not a generic formulation available at the time of writing.
Lisdexamfetamine is a prodrug, meaning it isn't an active drug by itself. Instead it is a combination of the actual active drug, dextroamphetamine, and a molecule of lysine, an amino acid. This was done to make a form of dextroamphetamine with lower potential for abuse. After lisdexamfetamine is absorbed from the GI tract, enzymes in your red blood cells remove the lysine molecule and free the now active dextroamphetamine.
Dextroamphetamine, as well as Vyvanse, are prescription-only, Schedule II controlled substances in the United States. This means that these drugs have a high potential for abuse and dependence, but have legitimate medical uses that allow them to be safely prescribed by a doctor.
ADHD/BED (Binge Eating Disorder)
If you're struggling with ADHD/BED, it's really important that you discuss this and other treatment options available to you with your physician, psychiatrist, or other healthcare professional you see for these issues. This drug, and most others for ADHD, can only be prescribed by a physician who is treating you.
If you haven't seen or been diagnosed with these conditions by a mental health professional, you should be aware that these drugs and the many helpful non-drug treatment options will not be available to you until you do. As a 'just in case you were wondering' disclaimer, I strongly advise against self-medication or obtaining prescription drugs through illicit sources. Not only is it illegal to obtain or possess controlled drugs that have not been prescribed to you, but stimulant drugs in particular can be extremely dangerous and habit-forming if misused.
How Old Do You Need To Be To Get Prescribed Vyvanse?
Regarding the age issue, this medication is approved for treatment of ADHD in patients 6 years of age and older, and for treating BED in adults. However, doctors are not bound by the indications the FDA has approved, and they can prescribe what they feel is medically appropriate for the patient they're treating.
There may be some additional paperwork or restrictions depending on your state of residence, as some states are enacting stricter regulations on controlled substance prescribing. If this is the case though, your doctor will let you know, so start by talking with them about your treatment options.