In my family there were two boys and two girls, and I am the youngest by a gap of 9.5 years. Yes, I was a lovely
surprise.

The big age gap meant that I had no one to play Barbie or My Little Pony with me, though there was no shortage of Lego playmates. Still isn't.
I was also pretty indulged and maybe over protected, only not just by my parents but also the three older siblings. I felt this the hardest when I went away to university, and felt the collective anxiety of five adults worrying that I'd cope, followed by years of spontaneous weekend visitors, and checking up phone calls disguised as quick hellos. This got many times worse after I had a serious illness, and has only recently simmered down a little.
One positive effect I think the large gap in ages has had is that I've always been comfortable with older people and now at 28, I've friends of all ages from contemporaries and younger, to 65 and older. I've never been intimidated working with older colleagues in the way I've seen some be, and maybe that's a result too.
How about you? Youngest, middle, eldest or only, how do you think you've been affected by your birth order?