Oh to be young and not have to think of being old.
How you behave DOES have a knock on affect of youe late life, quality and not quantity. I am afraid life isnt like that. At your age there wasn't as much knowledge about what we eat as there is now.
There is a link about what you eat to the quality of your later life.
So yes, enjoy now, but there will be 20 and 30 years further down the line where what you do now will affect the quality of your old age.
while being young, your body can cope with small amounts of certain things, eg alcohol as a prime example. over long term exposure/build up and age your body wont.
when you are young, your body can hope with the fat from foods better as you will have a higher metabolism when younger than older
same as with alcohol.
same with sugar - of which it can cause diabetes later in life. not too up on it overly much but , if u get ur body used to something it is harder when its not there/able to be processed
kinda the same as the stress response system - short term its fine, the body can cope. longer term longer exposure - the body gets run down, the resources available for the "action" diminish over time (not easily replenished)
hope u can see the point im tryna make here.