It could just be a combination of lack of light and age. Older needles and needles that don't get enough light die off. Conifer needles don't stay on the tree for ever, they all have a life span (some 2 years and some 4). This is the time of year for it too. If you find a pine tree to look at the inner most needles should be brown and falling off right now. If the needles from several year's growth and/or needles all start to fall at the same time then there is likely something more to fear. As for when it was planted.... the timing was really bad.
