I was today years old

I have never seen that Mark in my life

Or you could read use by/best before dates

I've had stuff for years

I always thought this is how many times you can use it before it runs out.
Kinda like the servings in a meal

I knew that since 2011 when I started work experience at a pharmacy and they explained it to us

How old were you when you found out it doesn't really matter as long as there are no significant changes in the product's texture, color or feel