JSON: go with the more standard JSON, "special delimiters" sounds brittle --> old fart loses
customers: don't solve their problem unless they paid for it or it's very small (<1hr). If it's a good customer they'll understand, bad customer will ask for more and more --> old fart wins
functionality: restrict if it's a headache to support unless it's something everyone else has already has --> tie, old fart and young gun should discuss it
genericness: big warning sign! In my first few years I was always building frameworks, now I solve problems. When the time comes to build a framework you'll know it but it takes many years to develop that wisdom --> old fart wins
To make matters a little harder the old fart seems to naturally have encyclopedic knowledge or was forced to develop it in a day and age of printed manuals (I remember those days and am glad they are gone!) The current generation of programmers has less need for rote memorization but keep in mind that there's some value in encyclopedic knowledge beyond the pure facts. If you know a lot of stuff without having to look it up your brain also becomes better at algorithmic thinking because you have more data to practice on. Sadly, my own memory has never been so great.