So are you saying the op may be right to be a little concerned?
I am saying the OP should be careful when exploring what she wants to believe to be the correct answer to her question
Anecdotes are not facts, but they can convince us that we "know stuff to be true" when if fact ...we don't. In some cases in our false state of "knowing stuff" we can go on to apply cod psychology that will impact how we evaluate each child's behaviours via fixed and vastly different filters based on birth order expectations. In most cases it won't cause any major issues, it will be a benign error of assessing on's expertise and not much else.
But not always.
For example.
An older child being responsible in a specific context may be ascribed to birth order and go uncommented upon because there is an expectation based on the false premise that this is the natural order of things due to them being the eldest. Whereas when they fail to be responsible in a wholly typical age/stage related manner, they may get it far more in the neck and have have far less slack cut because "birth order thinking" trumps bearing in mind their state of development.
Conversely in similar contexts the youngest may enjoy high praise for responsibility where they should be displaying an age specific capacity anyway, and get off scott free when they don't, with all sorts of excuses made for them.
BUT It doesn't follow that the eldest will the grow up responsible and the younger not so much. However it does make it hard for the family to see their now adult children as they actually are.
Case in point BIL is still seen as the responsible one and my husband the irresponsible baby. And how they are treated and are spoken to reflects that.
All this despite BIL being six figures in debt, his marriage shredded, his child deeply confused and his business on the point of folding ...all due to poor impulse control and heart not head thinking.
Dh on the other hand is still written off and dismissed as irresponsible, despite owning his home outright, being debt free and prudent with money, in a happy, stable marriage of long standing, with a kid doing well and a business that is surviving the economic crisis due to forward planning.
All the tangible evidence points to one reality, but the family and the "children" themselves see an imaginary reality based on ...a load of bollocks basically.
None of which does anybody any good in terms of family relations and self image, not least because you can't stop making the same mistakes again and again if you are always being told that the actual primary cause is not an ill from which you suffer due to your "birth order" birthright.
I think we need to challenge the idea that it's birth order that creates "issues" or "pre-ordained outcomes" and focus more on the potential disadvantages created thanks to the assumption that birth order matters. A false premise potentially responsible for leading to us conditioning ourselves to stereotype and pigeonhole our children and conditioning our children's self image.