Fructose is a valuable and needed nutrient. It is not the fructose that is the problem but the overly generous supply found in our manufactured foods. Fructose found in fruits and vegetables is slowly absorbed into the blood stream, its absorption blunted by the soluble fibre naturally found in these foods.
Whether you are young or old, it is important to listen to your body. Rest and recovery are just as important or potentially even more important than the training itself.