Is it in a container or in the ground? did you buy it as a standard, only it looks as if all the growth comes from the top of a straight stem, although its hard to be sure from the pics you've shown. Not sure if I can see a graft point at the base of all those stems in the second picture...?

It does look like a standard. don't prune below the graft point.
in the autumn I'd prune about 1/3 [evenly spread around the plant ]of the stems back to just short of the main trunk. new growth will then happen and the following year reduce another 1/3 etc.
this should rejuvenate it.

make sure it gets plenty of water as it is against a fence and a balanced feed too.