To keep it simple...
This might work?
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; Tempty.kix
; Empty the %temp% folder (delete all files older than '$keepdays' days)
; Version 1.00

break on

; init
$tmpdir = ExpandEnvironmentVars("%temp%")
if (substr($tmpdir, len($tmpdir), 1) = "\")
$tmpdir = substr($tmpdir, 1, len($tmpdir) - 1)
endif
$monthdays = 31,28,31,30,31,30,31,31,30,31,30,31
$keepdays = 15

; calculate today's serial date
$curyear = val(@year) - 2000
$curmonth = val(@monthno) - 1
$curday = val(@mdayno)
$curdate = 365 * $curyear
for $dummy = 0 to $curmonth - 1
$curdate = $curdate + $monthdays[$dummy]
next $dummy
$curdate = $curdate + $curday ; number of days since 01/01/2000

; dir files in %temp% dir
$myfile = dir($tmpdir)
while $myfile <> "" and @error = 0
if exist("$tmpdir\$myfile\") = 0
; calculate file's serial date
$myfiledate = GetFileTime("$tmpdir\$myfile")
if $myfiledate = ""
$filedate = $curdate
else
$fileyear = val(substr($myfiledate, 1, 4)) - 2000
if $fileyear < 0
$fileyear = 0
endif
$filemonth = val(substr($myfiledate, 6, 2)) - 1
$fileday = val(substr($myfiledate, 9, 2))
$filedate = 365 * $fileyear
for $dummy = 0 to $filemonth - 1
$filedate = $filedate + $monthdays[$dummy]
next $dummy
$filedate = $filedate + $fileday ; number of days since 01/01/2000
endif
; delete file if older than $keepdays days
if $filedate < $curdate - $keepdays
del "$tmpdir\$myfile"
endif
endif
$myfile = dir()
loop

; end script
:the_end
; That's All, Folks!

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