From age to age, nothing changes, and yet everything ..... is completely different

Ageing gracefully is one thing but when do we start to worry about this? Usually its when we start seeing the signs of ageing and its already getting late. They say that our bodies continue to peak until we are 25 and then after that its pretty much a downhill course. Surely there are those who can be obese at 25 and then by 30 be fit but its still only the best you can be at 30 rather then the best you could have been at 25.
Anyhow i find age creeps up on us quickly, as we start to near 25+ i have friends who claim they cant work as well hungover as they used to. Or is it that our jobs have actually become real jobs and now we have to actually do stuff rather than just fake it. There are small wrinkles, frekles, and for guys gray hair. Its scary really jsut when you thought you were coming out of being young youre already showing signs that you are old! Sometimes I wonder if the fact that there is sunscreen in my moisturizer that ill age better than my parents did? Although now the sun is stronger than back then.
Point is i think one day... well jsut wake up and well be old and we'll have no clue how we got there.