The other answers are misleading, so here is my take:
Yes, you should block IPv6 on the machines firewall or disable IPv6 on the machine altogether.
Here is why:
While the router may not support IPv6 (at this moment) and thus no IPv6 traffic is routed from external devices, the router does act as a Level 2 switch as well, so internally - because IPv6 works fine without a DHCP server - IPv6 traffic might work fine.
Now, since IPv6 is the only way to access some services today, one of your users might establish a IPv6 tunnel through IPv4 (which is possible and not very hard to do) to use this services.
If now the tunnel and/or the machine is badly configured, if may act as an IPv6 router through the IPv4 connection, turning the tides on the whole „IPv6 packets cannot reach that machine“.
It is also worth noting that even leaving the ports open to internal users might pose a security risk. This usually applies to people now knowing about IPv6 being enabled and defining firewall rules for IPv4 and think they are done, until whatever malware (android? Those are basically unpatched carriers of malware to begin with) gains access to your network.