The 2.0 litre EA888 engine in the GTI has a timing chain which is a non-serviceable item. The chain can stretch with age and mileage but that shouldn’t be an issue on a 5 year old car that’s only covered 24.5k miles that been well maintained / serviced in line with VW’s recommendations. As the car gets older, then it would be prudent for the chain to be inspected for signs of stretch, and then replace as appropriate, but replacement shouldn’t be necessary for a good few years yet.