I have lots of old data in my company file. Is there any way to start fresh without having to open a second quickbooks account?
Only desktop versions have a condense data utility. You cannot even easily create a copy of your current company let alone one for just a certain timeframe.
You could download a free trial of desktop, export your company to desktop, condense data and import into a new company, then cancel your old company. Even when you cancel paying for a QBO subscription your data does not get deleted until day 366.