How to kill all screens that has been up longer then 3 weeks?

Im creating a script that i am executing every night at 03.00 that will kill all screens that has been running longer than 3 weeks.

anyone done anything similar that can help? If you got a script or suggestion to a better method please help by posting :)

I was thinking maybe somthing like this.

First do a dump to textfile

ps -U username -ef | grep SCREEN >> dump.txt

then do a loop running through all lines of dump.txt with a regex and putting pid of the prosseses with STIME > 3weeksago in a array.

then do a kill loop on the array result.

edit: added script i ended up with

this is the script i ended up with, im killing all screens that has been opend longer than 30days buy user 1002.

#!/bin/bash

clear
echo "Starting Screen cleanup script this will stop any screens older then 30 days";
echo "Starting in 5 seconds, press ctrl-c to cancel";

    c=1
    while [ $c -le 5 ]
    do
    echo "start $c "
    sleep 1
    ((c++))
    done

    first()
    {
    echo $1
    }

    second()
    {
    echo $2
    }

    third()
    {
    echo $3
    }

    COUNT=0

    ps -e -o "pid etime comm uid" | egrep '1002'  | egrep 'screen' | while read PID ETIME COMM
    do
    case "$ETIME" in
    *:* )

            DAYS=0
            HOURS=0
            MINUTES=0
            SECONDS=0

            case "$ETIME" in
            *-* )
                    X=`echo $ETIME | sed y/-/\ /`
                    DAYS=`first $X`
                    ETIME=`second $X`
                    ;;
            * )
                    ;;
            esac

            X=`echo $ETIME | sed y/:/\ /`

            case "$ETIME" in
            *:*:* )
                    HOURS=`first $X`
                    MINUTES=`second $X`
                    SECONDS=`third $X`
                    ;;
            *:* )
                    MINUTES=`first $X`
                    SECONDS=`second $X`
                    ;;
            *)
                    ;;
            esac

            HOURS=`echo $HOURS + \( $DAYS \* 24 \) | bc`
            MINUTES=`echo $MINUTES + \( 60 \* $HOURS \) | bc`
            SECONDS=`echo $SECONDS + \( 60 \* $MINUTES \) | bc`

            if test "$SECONDS" -gt "2592000"
            then
                    echo $PID $COMM 
                    echo "DIE-DIE-DIE--------------------->killing pid------>"$PID 
                    ((COUNT++))
                    kill -15 $PID
                    echo $COUNT
            fi
            ;;
    * )
            ;;
    esac
    done