I am a web designer and I don't have access to a bank-account (and therefore, credit/debit-card) and I am not old enough to open a bank-account yet. Could I use a Bitcoin wallet to receive money and store it there as long as I want (and possibly, send those Bitcoins) ? Paypal would be ok except they only allow you to receive a limited amount before you are required to connect your Paypal account to a bank-account.
You can utilize cash to purchase Visa, MasterCard or American Express prepaid gift cards, sell these for bitcoins, and then you can do the inverse when ready and sell the bitcoin for prepaid gift card which can be sold for cash.
A little bit of searching on the dark web; you can easily sell the prepaid gift cards for a bitcoins, for a small fee. Of course, before proceeding with any of this you’ll need to set up an off-line bitcoin wallet to have ready once you sell the prepaid gift cards for bitcoins.
When you’re ready to cash in your BitCoin you can simply do the exact inverse to extract bitcoin to prepaid gift card and then sell these for cash (a robust market for this on the dark web as well).
There you go: (cash > bitcoin | bitcoin > cash), with no Identification, bank accounts, debit/credit cards required.
(Cashing out Bitcoin to cash using Peer to Peer sale locally is much easier to buy and sell cash to bitcoin and vice versa (e.g. localbitcoins.com); however, depending on the amount of money, it can be more dangerous then the method above)
Could I use a Bitcoin wallet to receive money and store it there as long as I want (and possibly, send those Bitcoins) ?
Yes. You can buy Bitcoin at Bitcoin ATM where is located some places. You can find a Bitcoin ATM here. Some ATMs allow you to buy and sell coins, but some does not allow you to sell.