It is possible to method to create author subpages (www.example.com/auhtor/username/subpage-content)? After which to use separate templates to individuals pages?

Consider the documentation. You will find many different ways to get it done. The heirarchy gets into this order.

author-{nicename}.php - If the author's nice name were rami, WordPress would look for author-rami.php.
author-{id}.php - If the author's ID were 6, WordPress would look for author-6.php.
author.php