But your desire to interact with people around ideas sounds like Ne is more about others than it is about the ego. (The dom. is about the ego's goals, and the aux will be a bit more about supporting others).
Wanting to research it to pieces sounds more like it is for your own ego, and thus would fit dom. Ti. So once you do that, then you want to share it with others in the form of "ideas" [Ne], and since this is supporting what the ego likes, you will be excited about it.
It could be 50; it could be the 40's (since most people will seem to live to about the 80's or 90's these days).What's 'middle age'? It better be like 50 or something.
If Si is tertiary, then around the 20's (possibly teens), you will become very nostalgic about things retro. This will have a very childish sense to it, and SJ's may complain you remember things you are interested in, but not what is really important.How do I determine the influence of Si and Fe? I tend to be pretty tactful and aware of social obligations/customs but still tend to be reserved with people. Unless I'm in a Discussion, then it's like flipping on a switch...3 hours has passed and I'm still yapping about topic X.
Then again, minding manners could be the influence of my upbringing. When I was growing up, rudeness was utterly intolerable and would earn you a switch across the backside.
If it is inferior, this may come up later, like the 40''s or 50's, and before then, you might be very unconscious of the value of past knowledge and such.
If Fe is tertiary, then you will become more conscious of social things in early adulthood. It still won't likely be very mature, and may come off as childish. If it is inferior, then it will be a very vulnerable area you might avoid, but then in 40's you might become more appreciative or aware of social values.