I think it's something more to do with how many breaths we have left....time speeds up..

This is kind of true. It is actually how far we are from the time we took our first breath. For a two year old, 1 year more is 50% of life. For a 50 year old, 1 year more is 2% of life. The experience held by each in memory will understand that same year differently and looking back, 2% is not much considering how much has happened.