If you have been cleared for hyperthyroidism as a teen, are you still at risk later in age if many in your family have been diagnosed?

Yes. Hyperthyroidism can occur anytime even if you were tested negative in the past. If you have a strong family history and you are exhibiting signs and symptoms of hyperthyroidism, you need to see your doctor to be tested again.
Vigilance. Best to maintain vigilance over your thyroid health in concert with your doctor. Discuss with her the symptoms of hyperthyroidism; what to watch for, what you may experience, and maintain open communications to be sure you discover it if it ever does occur. This is a very treatable condition - all that is required is a diligent attention to your health.