New-NaUser and Set-NaUser do not currently have the ability to set minimum and maximum password ages. I have logged this request for consideration in a future release.
In order to get those properties returned, you need to use the "-GetCapabilities" switch on Get-NaUser:
PS C:\> Get-NaUser steven -GetCapabilities | fl *
Groups : {Administrators}
AllowedCapabilities : {login-*, cli-*, api-*, security-*}
Comment :
FullName :
Name : steven
PasswordMaximumAge : 4294967295
PasswordMaximumAgeTS : 10675199.02:48:05.4775807
PasswordMinimumAge : 0
PasswordMinimumAgeTS : 00:00:00
Rid : 131075
Status : enabled
UseradminGroups : {Administrators}
PasswordMaximumAgeSpecified : True
PasswordMinimumAgeSpecified : True
-Steven