My guess is it's a new one, or at least the engine is, if you mean the phillips bolts in the carterpanel as well ?
I replaced them all on my 1999 Whizzers with allen bolts fast so I could tighten them with more torque, the phillips heads were easily destroyed after one use, soft as butter...but as far as my knowledge goes the easiest way to determine the age is the engine/cilinder/head material: if it's all aluminium it's a newer one. Older engines were cast iron and steel and parts are not interchangeable with new models.