My hydrangea is about 6 years old. For the past 3 yrs I've noticed brown spots developing on leaves after it has bushed out in late Spring. The bush doesn't flower at all
Certified GKH Gardening Expert
It is likely a large leaf hydrangia, which will flower on old growth only. This will mean that if it freezes and dies back, then it may not flower.
Alternatively, if it is not a large leaf, then it could be starting an infection. These spots would indicate that. It would be very helpful if you can post a photo. This will help me identify the problem better.
I recommend adding dolomitic lime and wettable sulfur around it. This will help kill off any infection, as well as provide the plant with some commonly deficient nutrients at the same time.
This article will help: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm