Normally, it would not be void, but rather voidable at YOUR option since you were under age at the time and thus could not effectively give consent. However, if you used the account for some time after you became of age, then even you may be estopped from arguing that the agreement is void. Here is a copy of the service agreement. Section 6.1 lists the restricted activities and one of them is breaching the agreement and another is "Provide false, inaccurate or misleading Information". The intro to the agreement states that:
We may close, suspend, or limit your access to your Account or our Services, and/or limit access to your funds for up to 180 days if you carry out any Restricted Activities (as further set out in clause 6).
1.7 Eligibility. To be eligible for our Services, you must be at least 18 years old and a resident of one of the countries listed on the PayPal Worldwide page.
So, when you accepted the terms and conditions while under age, you misrepresented your eligibility to be a user.
If you used the account after you turned 18, then you do not have a case here and should just wait till the 180 period is over to get your money.
I know this is not the answer you wanted to hear, but I am assuming that you are paying for a professional and honest answer.
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