Mine is about 4 years old and yet to flower.... is something wrong with it?
The most common reason for lack of flowering is not enough sun. Do you have yours located in a full sun situation - 6 to 8 hours of sun daily?
Sumacs also need to be irrigated during dry spells. They prefer slightly acidic, well-drained, moist soil.
If you want fruit, you need more than one sumac. Their flowers are either male or female on separate plants, so you need both for pollination. These articles should help:
https://www.gardeningknowhow.com/ornamental/trees/sumac/sumac-tree-info.htm
https://web.extension.illinois.edu/shrubselector/detail_plant.cfm?PlantID=429