I already know one way (visa gift card) but are there any other ways a teen under 18 could buy a donation feature?
Well, I'm under 18 and have a Visa Debit Card I use for somethings. I would recommend giving cash to your parents and they buy with their Debit Card. For example, you want Water Feature, give $15 USD cash to your parents and then they purchase the feature with their card and number. That's what I do because normally my checking is 0.
Do note that if PayPal catches you under the age of 18, they will freeze your account... You can get your own type of bank card under the age of 18, but some parents do not allow it (I got my own card at 17)...and thankfully - at least in the past - you did not need PayPal to donate to ECC; it would just pay through PayPal, and only use your card. Other than a card, a gift card, and IGM, you would have to win contests/raffles/etc for "money" to buy donation features.
You can do one of two things.... One convince your parents to get you a DEBT card (under their name). With that you can just link up a PayPal and DA TAH!!!!! Or.. You can get yourself a Visa Gift Card and upon checkout, click "guest checkout". As long as you have activated your card (The website is on the card) Then just enter the card and... TA DAH!!!!