Sorting data in PowerShell

Working in powershell I am wondering how to Sort a txt file formated like

Smith,John,45
Jean,Rob,60

The code I have listed below sorts the Last names correctly but I cannot get the average age of all the names and also when I try to get the Age sorted output it only displays some of the names. Any suggestions on how to properly get these outputs?

#Average age of Data   
$fileLines = Get-Content -Path C:\PowerShell\m22.txt   
-split '\r?\n'

$fileLines | Measure-Object { [int] $_.age } -Average | ForEach-Object Average

#Last name sorted Output  
Get-Content -Path C:\PowerShell\m22.txt | Sort-Object

#Age sorted Output  
$fileLines = Get-Content -Path C:\PowerShell\m22.txt  
-split '\r?\n'

$fileLines | Sort-Object -Descending { [int] ($_ -split ',')[-1] }