I'm pretty sure the maximum age is around 30. If you choose the perfect personal training, then you'll have results. Of course, everything depends from a case to another. It cannot be a general formula for everything. You can try contacting a personal trainer and see his point of view. After that, everything will be clearer, for you. The only minus here is the age. The older someone is, the harder it is for him to train and have better results. In the end, everything depends on the situation, as I've said before.