I had a quick scout around a few Presbyterian records while I was at the archives yesterday. I did find one Robert Young in Norham but baptised 1772 he’s a bit earlier than the one you are looking for.
What I did find, and have not noticed before, was that some churches had listed the marriages of their congregation even though they were not married in that church. Several Scottish places appeared regularly as venues and it might help you in your search for the marriage. They were Ladykirk, Coldstream, Upsettlington, Swinton, Dunse (Duns) and Lamerton (Lamberton).
Christine