How to forecast labels forward 3 years
You dont specify explicitly how far in the future you want to make your predictions, but rather you do that implicitly when you make sure your model is robust and does not over-fit.

What does that mean?

Make sure that distribution of labels with your available independent varaibles has similiar distributions of that what you expect in future. You cant expect your model to learn patterns that were not there in the first place. So variables that show same information for distinct median gross rent values 3 years in the future are what you want to include.