Itc in gst

Hi, We are registered traders of Electronic Components in Karnataka under KVAT/CST and now got migrated to GST. We have stocks as on June 30th 2017 which are bought more than a year back and within a year as well but none of them are suffered any Excise Duty when we bought them. Our question is can we claim ITC on the closing stocks though there is no Excise when purchased? If eligible is the ITC available on entire stock irrespective of time of purchase? Please clarify.. Thanking you in advance, Venkat