Q.Greenspire Little Leaf Linden
Our home has the above tree (to the best of our knowledge). Could you please tell me:
1) How long does it take to “mature”?
2) What is the mature size?
3) Is there any time of year in Zone 5 where low hanging branches could be pruned, so as not to have a person hit in the face when using a riding lawn mower?
Thank you.

The Little Leaf Linden grows at a medium rate at 13" to 24" a year.
It is best to prune a deciduous tree in it's dormant period.
This causes less stress on a tree.
Here are a couple of links for you.
https://www.gardeningknowhow.com/ornamental/trees/linden/linden-tree-information.htm
https://extension.unh.edu/resources/files/Resource000595_Rep617.pdf