Does it ever flower? How large is it? It looks a bit like a lime tree (not the citrus fruit type...but Tillia).

never flowered here is another pic

about 4.5 feet high

Does it do anything else interesting? Fall colour, perhaps? (it still looks like Lime to me!)

no it does not do anything that I can recall....don't think it is lime though....I did know the name but forgot..that is not it...wah!

It looks almost like some forms of mulberry. Does it get little green catkins in spring, just before the leaves come out? If it is a male, it won't have berries.

not sure what a catkin is ....at some point last yr there were red spiky things on the leaves i think

These catkins look like 1-2 cm long pieces of fat, bright, lime green chenille growing off the twigs.

no, no catkins

Red spiky things could be lime leaf gall mites. Check out the photo on this web-page.
http://www.aphotofauna.com/mite_gall_eriophyes_tiliae_lime_leaf.html

If this is what the spiky things looked like, then it must be lime.