Is it possible to restore my old WhatsApp messages which I have deleted earlier from my whatsapp if yes how can I restore them?
There are usually two ways of restoring your messages. Local backup or Google drive backup.
Local backups are stored on your phone for up to 7 days only. After that, they are automatically deleted. Therefore, if more then 7 days have passed since you deleted the messages and you haven't manually saved those files, you will not be able to restore the deleted messaged that way.
Google drive backups on the other hand, are made periodically in the time specified by you. Check your WhatsApp settings to see when the last backup was made. To do that, open WhatsApp, go to settings -> chats -> backups. If the date of the last Google drive backup is before the time that you have deleted the messages, then you can still restore them.
To restore your Google drive backup, follow the steps provided by WhatsApp's FAQ page here
Have in mind that you will lose all the messages that were written after the time of backup.
Otherwise, if the conditions above don't match, you won't be able to restore those messages.