Unable to Validate Your Purchase Date

Are there any issues in the future I'll be concern of?

Oh yes. That's a bad sign.

Even though it was written for iPhones and iPads, The All Too Common SAD Reality of Buying a Used iPad/iPhone - Apple Community is equally applicable in principle to Macs. It's quite likely that Mac won't be usable to you, and you may not discover that until such time it's necessary to reinstall or update macOS, long after the seller is gone with your money.

Walk away from that deal.

In addition to John Galt's excellent comments, should you go ahead and purchase this laptop, the other issue is if it does require any repairs, any warranty would only be valid in the U.S. as Apple does not provide an international warranty. That would mean, you you need to bring the laptop back to the U.S. to get those repairs done.

I'm in total agreement with John on this one. Walk away from this "deal."