Underage rhymes with:
alderidge, acreage, alderidge, amperage, average, betteridge, beverage, beveridge, brokerage, deatherage, detherage, everage, hemorrhage, leverage, pilferage, seigniorage, sewerage, stockbrokerage
Underage sounds like:
under-age, undercook, undergo, undergoes, undersea, underseas, underuse, undress