Either way, the whole idea and concept in general just sounds uncomfortable to me.
Befriending younger females for the sole purpose of hoping to try for a relationship once they are a few tears older doesn't seem right.
Besides, Monstercrack, what is your plan once they are older? You get older as well.
This is why a 4 year age difference won't work for you. When you're 18 she'll still be 14 and that means you are friends with a 14 year old female for the purpose of a possible relationship in the future. When you're 20, she's 16. And so on.
You'd have to wait until she's 18 (6 years) before it becomes even the least bit acceptable (you being 22).
This is a botched idea/plan from the very beginning. A lot of your posts frequently indicate that you frequently move on to other people and between people for possible friendships in extremely short amounts of time - some posts I've seen from you basically say one month you've made a new friend, the next they hate you or you've broken contact with them.
If you don't have the ability or patience to consistently wait and maintain a friendship for at least 2 years, how do you expect to do so with a younger female for 6 years until she's 18?
And I'm not tying to be overly critical, harsh, or judgementel, but actually encouraging you to reflect on just what your own ideas/plans are.
And this is coming from someone who relates. My current girlfriend is a year younger, my ex was 19, I have a 19 year old friend, and a 14 year old friend. I always struggled with making friends a similar age in the past.