Is my Certificate still valid?

You can check this at: https://lhcb-web-dirac.cern.ch/DIRAC/LHCb-Production/lhcb_user/systems/framework/manageProxies

or you can execute:

openssl x509 -text -noout -in ~/.globus/usercert.pem | grep "Not After"

which will give you the expiration date.