Prior to unsupervised clustering, how do I compare time series data of different time intervals?

My data has monthly observations of hundreds of thousands of policies and I want to cluster the policies into segments. In order to boil the data into one-row-per-policy, my plan is to extract features from the time series columns, but the policies vary from 1 month of data to 20 years and even if we have two 5 year policies, an issue date of 2000 results in different observed behaviors than one issued in 2015. How do I get a …

clustering data datascience prior time time series unsupervised