You need to get this clear though. Are you looking for a wallet or an exchange? Because if you're going to buy and sell the coins pretty frequently and you're not planning on holding the coins as for speculation, then an exchange like Coinbase would probably fit you best. Also, what do you mean by "I want to buy and sell cryptocurrency?". Do you mean you're going to buy and sell to people in your local area? Or were you referring to day trading?
You really don't expect something with little to no fees though, the best you can do is to minimize the fees by using something like Coinbase Pro, Coinbase's spot exchange(the exchange with charts and stuff).
The "best" exchange to use for you really depends on what country you're in though. But if Coinbase allows users from your country, then it's probably your best bet. Though I'm really not sure if they have an age requirement.
If you want to read more concerning wallets:
EDIT: Yep. Coinbase requires you to be at least 18.
From
https://www.coinbase.com/legal/user_agreement:
"To be eligible to use any of the Coinbase Services, you must be at least 18 years old and reside in a country in which the relevant Coinbase Services are accessible."Unfortunately for you, I assume most of the reputable exchanges like Kraken, Gemini, etc, also requires 18 years of age. Try buying from services like Bisq[1] I guess? Though you might need to wait a while to get coins in decent prices.
[1]
https://bisq.com/