We also planted a half-dozen hazelnuts years ago to see how they’d like living at out place. They have been very slow to produce – this year the first nuts have appeared.
I’m not sure if this is normal for first fruiting but 4-5 years seems a bit long – we have peach trees that have produced fruit faster than that. We may have a place for them as the shrubs below the understory in the developing shade strip down the center of the back pasture.