Jeter and Boggs are entirely different in terms of hitting style, so the comparison isn't good. Ripken and Chipper are both better; Ripken is a better comp than Chipper. Chipper walked a lot, had a great eye, so that helped him to age gracefully. I wouldn't expect A-Rod to look as good as he did. But A-Rod is also just straight-up better than anybody on that list. Career OPS+ of 143.
And in spite of your denial of it, at his age you're always somewhat tired as a professional athlete. The day-in, day-out grind is definitely wearing on a guy in his mid-30s or older. He will come out next season as fresh as he's been in years. By mid-season it won't matter anymore, but if he starts hot it's a confidence-builder. It's easier to hit when you're loose and confidence, you know that. So yes, I think starting out feeling really healthy and strong is potentially very important.
Note that I never said I expect A-Rod to finish out his contract strong. I said I think he has one more 28-30 homer year left in him. And I do.