Hi, No it is not possible to limit a sub-domains space and bandwidth usage in current versions of cPanel. You can limit the primary domain's space and bandwidth usage but the bandwidth and disk would be shared between the two domains. You can also remove the domain as a sub-domain and add it as primary domain which will give you all the features of a regular domain.
My local Cpanel expert is not at home at this moment to provide you with further details, but I believe he played with that setting a while back, however you need root access to the server and modify a configuration file via SSH.