When I was about 14 my dad bought me a 13' Whaler with a 20hp motor. Several years later we sold the 13' and bought a 15 Whaler with a 55hp engine. I used it through high school but did have to replace the engine. Repowered with a 48hp engine, I kept the boat through college. After that I bought bigger boats, up to a 28 Formula with twin engines. Then gas went to $4/gallon so I sold it.
I went back to the basics and bought a 170 Montauk in 2008. It gets great gas mileage and should last a long time.