Life assurance is a good thing to have and is always better to take out at an early age as prices increase as you get older but it seems strange that your bank has not forst confirmed your need or relevance for the policy and also that they would recommend a DTA.
DTA is normally taken out against a repayment mortgage to ensure that the mortgage would be fully paid in the event of your death, this said, if you have no wishes to pass your assets on to anyone after your death then there is no reason to do this.
Likewise, if you have no property, mortgage etc and you have no wish to pass anything onto either relatives, children or friends then there is no real reason to have a [policy of any kind in your name. If youdo want to leave something behind then mayube you could look into it a bit more...but I am not sure why you would want to take out a decreasing term assurance as this will just reduce in value over the term