My son got this toy at 18 months, and it kept his interest for nearly 6 months.  I added on the amusement park after 3 months, and he figured out directions, speed, on and off, how to set gears against each other so they would start spinning, and he even learnt to look at the back of each gear to see whether it could go into the middle part on the motor cog.  The toy and he were practically inseparable for weeks, and its been known to have stayed on for the whole day at a time...