Your older sibling broke in more than the shoes. They broke in the rules you got to skip.

First children run the experiment. An older sibling tested every rule, absorbed the refusals and made the first version of each argument, so the terms you inherited were negotiated by somebody else before you arrived. That work was done with no credit and mostly no thanks, and they got the stricter edition of everything while doing it. The order you were born in is not a merit.

Say that to your older sibling once, plainly. Then look at what your younger ones are currently fighting for, and see whether you can take their side instead of enjoying the easier terms.