The paytm app version that I can see on playstore is 10.19.0.
So most probably you are using a phone with outdated android version and. Paytm stooped updating the app for tat version..
There is nothing you can do except trying to root your phone and install custom android rom if supported.
If yours is Samsung phone by any chance, try downloading Paytm app using Samsung Galaxy app instead of Playstore.And then login