From my own mother:
Some thoughts about Aunt Hood. My first niece was Kirsten. I was 18 years old and was on McNeil Island when I got the phone call. She was adorable, only 5 lb 12 oz. They visited a lot and when I got my job the next year, I used to give Ginny money for Easter candy and I remember buying tennis shoes for Kirsten’s one year. I always used to send birthday cards, this year I was remiss. Kirsten really appreciated it. All you have to do is just be yourself and the baby will love you.
One notable difference: I am 10 years older than my own mother was when she became an aunt. I can see advantages and disadvantages to this age difference. Most likely I have more means than my 18 year old mother did (better/more gifts?), but I think the older I am, the less cool I automatically become in the eyes of my nephew. I might be more mature and responsible but perhaps less fun?