Is age a hindrance of getting acceptance in a PhD program?
I think you can rest easy (and work hard). There are a lot of people who decide to work toward a doctorate later in life. Depending on what your background is, you can bring a lot of experience to the process. 

While most programs depend on a certain amount of knowledge in the field that undergraduates normally come with, mostly breadth and a bit of depth, a person who has worked in a field and kept up with the changes required of a professional probably won't be handicapped. 

However, as with anyone else, you need to make a case that you are both prepared and have the drive to plunge deeply into research. Everyone is a bit different, but age, itself, is no barrier.