Welcome to the Linux world. Actually crontab is a very elegant way of doing things, and you should follow the advice you got so far. It is the Linux way of scheduling tasks. Unless you want to code the wheel again just use crontab.
The command you are looking for is:
find /path/to/your/folder -mtime +[days old]
eg:
sysadmin@omg:~/sync/0434$ find . -mtime +180
./201305_10min.csv
./201308_10min.csv
./201307_10min.csv
./201303_10min.csv
./201312_10min.csv
./201301_10min.csv
./201311_10min.csv
./201302_10min.csv
./201306_10min.csv
./201304_10min.csv
./201211_10min.csv
./201401_10min.csv
./201309_10min.csv
./201212_10min.csv
./201310_10min.csv
This will show all files older than 180 days old...
To delete these files I would add:
find . -mtime +180 | xargs rm
xargs will pass each line returned from find to rm as an argument
And if I cron this I will never be bothered with files older than 180 days on my system anymore.
The web-based interface is a whole subject itself. You should be familiar with HTML forms, GET/POST methods to communicate with the client and use probably PHP method ftp_put to upload to your server.
http://www.w3schools.com/html/html_forms.asp
http://php.net/manual/en/function.ftp-put.php
Also note that pointing your web server to your ftp directory will list its contents (files) which are downloadable with a click so again you don't need to code a web interface yourself. For example try:
sudo apt-get install apache2
sudo rm /var/www/index.html
sudo cp -r /tmp/* /var/www
sudo chown -R www-data:www-data /var/www
Type-in your server's address in your browser:
http://your-server-IP
You should see something similar to your requirement:
2) Allow another user to download the file from the same interface
I hope you find this useful and introductory to Linux. Appart the web interface to upload files -which is purely web-design, not linux question, ask anything that seems confusing to you in the comments. I will try to make it clear for you. But please do learn at least which distribution you are using not 'some variation of Linux'.