Trend is mainly used for time, but technically is possible to group by any field other than time fields. For the case of integers representing years, ChartFactor will handle them as time if possible. THis is not the case of the Time Slider which strictly works with time.
In that case if you don’t have time fields then you would need to create a derived field for time. See this forum entry: How to create a derived field for time and docs. Alternatively, you could update your dataset on your data engine.