The listing agent has the ability to provide the seller with a list of buyers that they are entitled to a commission for if they buy during a set period of time. That is usually 180 days and the agent had about a week after the listing ended to give it to the seller in writing. If you never wrote an offer its unlikely that happened. My guess is you are probably free to go for it but would probably be better off having some level of representation to get you both through the process.

One additional point, even though ti may not be actively on the market it may still be under contract with the listing agent so you will want to make sure that isnt the case either.