Google provides an excellent set of public DNS servers but it won’t work on an native IPv6 address or transport. From the official google help pages:
Google Public DNS can respond to requests for IPv6 addresses (AAAA requests), but it does not yet support native IPv6 transport and cannot talk to IPv6-only authoritative nameservers. Clients should use IPv4 network connections to use Google Public DNS.
In other words you can get an AAAA IPv6 record using IPv4 transport only as google public dns server does not have native IPv6 address:
$ host -t aaaa softlayer.com 18.104.22.168
Using domain server: Name: 22.214.171.124 Address: 126.96.36.199#53 Aliases: softlayer.com has IPv6 address 2607:f0d0:1000:11:1::4