SQL Server 2016 Standard AlwaysOn group
While AlwaysOn/Availability Groups are a welcome edition to SQL Standard Edition 2016, the GUI is not supported for group creation. Try using the T-SQL code to create the group. Per Microsoft: https://msdn.microsoft.com/en-us/library/mt614935.aspx

"To create a basic availability group, use the CREATE AVAILABILITY GROUP transact-SQL command and specify the WITH BASIC option (the default is ADVANCED). For more information, see CREATE AVAILABILITY GROUP (Transact-SQL). At this time, there is no UI support to create basic availability groups in SQL Server Management Studio."

The GUI is spamming the Advanced group used by Enterprise Edition (to your Standard Edition) while, Standard Edition only supports Basic.