Your problem is not „speaking tcl“, but how are you going to find out the last active date?
if you know, where it is specified, it’s a simple for each loop, otherwise (and this is the only one known possibility for me) you have to document interface status periodically, probably each hour, and evaluate this data for required time period. Afterward you can use this data to disable unused interface.
But TCL running on some network device isn’t the right tool for data analysis, I would suggest to look for some external tool
