There is no first, or everything is a first. Life is one first after the other, again and again and again and again. Ask me about the first time I urinated on a tree. I don't remember.
Every moment is a first somehow. Just keep doing firsts. Until the first time you die.
Our ideas and societies and morals and perceptions are so polarised so often. It's easy to place ourselves and have ourselves be placed by others into little categories that become lenses to be seen through, to be known through. Designating some things as important is natural, and I know I have done it to various bits of my life and personality for lots of good reasons, but I also know I have done it unavoidably in ways that are ultimately not helpful.
We have so much of a 'rite of passage' and goals-driven culture that pushes us to make bucket lists and visit as many countries as possible and put 'first kiss' in a trophy case, and it fosters so much sadness. What's a first kiss compared to a thousand kisses all different in feeling, tactility, location, etc? What's the first time I rode a rollercoaster where I was 93% spooked compared to all the subsequent times I rode 'em and got to notice the way the wind rushed around me with a sense of calm excitement and relish for the twists of the track that feel so much better now that they are known to me? Firsts can get lost.
Firsts aren't inherently more important than the rest of your life, than all the things repeating and circling and growing and being chosen again, and again, and again.
First, last, everything, whatever.