Again, I completely agree. I have a younger sister - she's almost 7 years younger than me - and with younger siblings I think you just tend to try and tell them what to do. Because you want to protect them and keep them from making the same mistakes you made... and with my sister, I used to be her role model for a long time and I think it was weird for me to adjust when that changed.
But as you said, when you grow up you need to find a new balance in your relationship with your siblings, one that is more equal but that doesn't make it any weaker or whatever. My sister and me are best friends nowadays and I ask her for advice in the same way she would ask me.