If you want to obtain bitcoin and you are underage,
Ask Your Parents, to use an exchange like Kraken,(sorry Coinbase, not recommending you), and many other exchanges. They will usually use KYC regulations, and require your id or other documents.
Use LocalBitcoins.com or Paxful.com . Psssh, who needs KYC, when you can buy BTC without it. It is not that simple however, LBC and Paxful, use an escrow service, meaning that the bitcoins the seller has and you need to give him your payment method, be it Paypal or gift cards, in time before the escrow expires. I have lots of trades on both of these sites, and to verify that the seller is good, you need to, have prior sales with him/her, or look at his/her's profile and see the positive and negative feedback. The fees on both of these sites are enormous, even if you are using small amounts. You can use many options to buy on both of these sites, including, ITunes gift cards, Xbox GC's, Prepaid Visa and Amex Cards, Paypal, Amazon Gift Cards and many more. Remember, if you have bitcoin sin the wallets of this website, amke sure to transfer it to your personal wallet or others, I'll get into that later.
- Use r/Cash4Cash, and r/giftcardexchange. Well if you are reading this, better just stay here, on both of these subreddits you can trade prepaid gc's or just regular GCs for Bitcoin, Cryptocurrency, or just straight up Paypal or Square Cash money. On these subreddits, you want to verify the user you are trading with, NEVER trade with low karma/throwaway accounts, and use r/GCXRep, and r/C4CRep, so you know other people are real and other people know you are real and not a scammer.
- Work for it, Some places on the internet give you bitcoin for working for it, if you can do the tasks on these sites, however big or small, you can get BTC, like r/Jobs4Bitcoins, Coinality.com, Cryptogrind.com, and r/slavelabour.
You might find out that some of the jobs might be too complex for you. But scroll a bit and you will find some easier ones.
If you want to use these freelance sites effectively, then try to up your typing skills, get better research skills, learn about graphic design, or if you are good at illustrations, use these to your advantages. r/Slavelabour is for extremely small tasks, that pay.
- Storing your BTC effectively and privately. Remember the age old Bitcoin mantra, Not your keys, Not your Bitcoin, Your Keys, Your Bitcoin, this means that your private keys, which is the thing you need to access your wallet and sign transactions, you should be in control of, on all exchanges, like Coinbase, Kraken, and Bitfinex, you are not in control of your private keys, meaning that they can shut down your account for many reasons, or they can be hacked. This also applies to your 12 Word Seed or Mnemonic Phrase that you get when you open a wallet, KEEP IT SAFE, IF YOU LOSE EITHER OF THESE, YOUR BTC IS EFFECTIVELY LOST, read up on it more here https://en.bitcoin.it/wiki/Seed_phrase
and here https://en.bitcoin.it/wiki/Private_key , if you want to get the best wallets for storing your btc go here https://bitcoin.org/en/choose-your-wallet , but my favorite one is Electrum personally. Although this is not on bitcoin.org, I suggest Exodus wallet for multi-cryptocurrency support, if you are looking to invest in more.
Another danger you have to face is downloading btc wallets on malware infested computers, this will affect in your BTC being lost, so don't do it.
The worst way to store your bitcoins is on the internet, web wallets, like Blockchain.info where you are not in control of your keys, do the same things like exchanges mentioned before, where your wallets can be shut down and can, and, were hacked.
The two best ways to store your bitcoins are on Hardware wallets like Trezor, Keepkey, and Ledger, where your BTC is stored on physical hardware, the only downside is that it costs money, if your parents are cool with crypto, they probably will let you have one. If they are not, try to get one delivered to a friends house who consents, the Ledger in particular looks like any unsuspecting flash drive. Make sure you are buying from the official websites of the wallets and not other ways, counterfeit Hardware wallets have security defects. The next best way, are paper wallets like on bitaddress.com, where your bitcoin public key and private key are on paper and not on any computers, it is essential that you turn off WiFi on this site and make sure nobody is spying on you. Paper wallets have a problem that sort of defeats the purpose of using it that to to take out the funds you need to use a web wallet. But, still for people who want privacy in storing btc and at about zero cost(apart from ink and a working printer) ,it works.
This applies to minors also, Never Invest More than You Can Afford To Lose, Don't put your entire allowance into BTC, if you are in it for the money, you will need to have patience. If you are not in it for the money, good job, you are about to venture into the world of cryptography and privacy.
TL:DR: If you want to get BTC when underage, ask your parents, or use LBC/Paxful and trade Gift Cards, Go on job boards that pay in BTC, and store BTC in safe Bitcoin.org sanctioned wallets.