Modern Vespa

I am a new member just joined and I have a question
how often do you have to change the oil on a vespa? I have a 50 and about 100 miles but it is 14 months old . Do I need to change oil?

Is that 100 miles total on the bike or 100 miles that you have ridden? If it is 100 miles on the bike, the first service would be about 600 miles, so you have a ways to go. The oil should be changed at least once a year. Where you are located has a bearing on how much riding you can do. If you live in a seasonly cold climate, you might want to change the oil at winter lay-up.

It's a small air cooled bike with no oil filter, so if you ride it as fast as it will go all the time, you might do well to change out the oil at 300 miles or so and then go to a pure synthetic 15-50 or 20-50. Small scooters abuse motor oil a lot more than larger ones. Piaggio's recommendations as far as service intervals and oil viscosities seem to be based on riding the bike in a perfect world, and one marketing ploy is to extend service intervals out as far as you possibly can.