2018 Cayman S delivered new to me January 2018, built September 2017. I just crossed 5,000 miles and the oil service message came on. This is less than the 10 k specified interval and less than one year of ownership/use. Oil fill still at max indicator. Did this come on because the car is one year from manufacture or does it somehow reflect conditions of use? The car is a toy and most of the miles could be described as spirited, some commuting but no stop and go.

 

It has nothing to do with "conditions of use" - it's time or mileage.
You're probably good to wait until the 10k mark if you want - but it's getting close to a year of use anyhow (3 months?) so may just want to take it in anyway.