So I have around 300 euros on my bank account and am 14 years old. Rarely buy stuff physically. Most of the things I buy are stuff online (e.g. games). I don't really like spending but my so called 'friends' spend all their money. I know not to spend a lot. But will it even make a difference if I do not spend on anything and collect all my pocket-money until I am an adult?

Keep in mind, you're still growing. Habits you make growing up tend to persist into adulthood. When you're an adult, do you want to be a consumer living payday-to-payday or do you want to be an investor with comfortable savings?

Starting savings when you're young makes an astonishing difference for retirement savings. Say for example you start saving $500 per month when you're 20 and earn an average of 8% per year. When you're 65, you'll have $2.7 million and be making more than $17k per month. Say instead you start when you're 30. Then you'll have $1.2 million and be making $7600 per month.

Getting a car at 16 or whatever might require a fat down payment as well as a steady job and a parent co-signing the loan, if you got a used 10,000 euros car perhaps you would be putting 2000 down, insurance is another thing that an be costly.

Certainly just building good savings habits will help you later in life, if you were suddenly just kicked out of the house at 18, having savings enough to pay rent would be handy.

isn't it better to save your money than spend it on things you do not need which would be wasteful.

If you don't especially want anything now, by all means hoard your money until you do.