Feeling Old

Many people have their physical abilities peak at about the age of 25 but I wonder what was mine. Why do I have that thought? It seems like I am always tired everyday. Might be my sleeping pattern, diet or my lack of exercise. However, I wonder how many people experience this too. Being tired everyday, it seems like I am old already. I just started my university after 2 years of army life, is it because of army that it made me feel like I have aged a lot? I wonder...