Dehydration is the key. I know when I worked out doors I would drink 1-1 1/2 gallons of water a day so when I drank on the weekends (16-20 beers on the boat during the day) I would not have any hangover on monday morning even without drinking any water. Now I drink about 1/2 gallon water/day and 3 beers will leave me feeling dehydrated even if I have a glass of water before bed. So rather than age I think it is the regular daily intake of "good" fluids (not coke,coffee,beer,etc , but water, juices,etc) that as we get older we stop being as active and eating as well as we did when we were younger and had to maintain that energy level.