Could I write what I am writing at 21 years old? Perhaps, but truthfully, it would not be as well seasoned or as deep. It wouldn't have the nuances and the grit that it has, because I was in deep trenches after 21 years old. Does age and writing correlate? I certainly believe so.
Toni Morrison adviced writers to turn 40 before attempting to write a debut novel. It has its advantages to write after a life long experienced. The hardest thing to do was finding the mindset, time and space for writing. I couldn't write yesterday because I my body hurt from yard work and hard work. I had to rest, because today I will find more time to write.
After finding the mindset, I had to find the age range of my audience, what age I wanted to write for. As we all grow, the child within often yearns to come out and play, and that dictates the genre and age range of your audience. For me, I am perpetually in 7th grade. It never swayed from 11-13 years old. The experiences I had at that age and younger was so prominent inside my mind that it stuck to me and held me dear. It gave me pleasure as I thought of those times and it gave me energy to keep writing.
Yesterday was gone, and I knew as we age, we were to forget the past, but I couldn't help but to hold on to my childhood years as much as I possibly could because it gave me joy. Not everything was perfect, but there were kindred spirits who kept me at joy and I remained in contact with them. My friends kept me alive back then, and they kept me alive still now.
As I write the work I was to write and called to write, I will remain in me, the child within, even as I age to 144.
Just write.