One account is AFAIK forever or until they keep getting donations(from big companies like google, so not much of a chance of running out of donations). You can also make multiple accounts, but be sure to register and login from them through different IPs.
BTW @OP I am getting problems on my VPS, my network(on VPS) has gotten "Limited" a couple of times, everytime I have to delete it and start a new instance to continue using my VPS, any solution?