Loric

I don't know diddly about your study/major/field so I cant really comment on all that.
 
I can say:
 
Lose "Since I want a kid" - no one cares about your entire life since birth. Simply say "I have always been interested in.." or "fascinated with.."
 
Preoccupation suggests OCD. OCD suggests mental illness. Mental illness is considered a "kiss of death" for admissions.
 
We all went to high school and had to take science and math. No one cares. Just delete that whole sentence. Really, your statement works fine without and seems to meander less.
 
Also, why is the question you want to answer - why do things age - important? You need to frame it a little. Why should I care? I don't know, maybe that's a huge topic of study at this school, but I dunno. Maybe it's inherently interesting anf something I should throw money at you for. I dunno. Tell me why.
 
And that's about as far as I can go with my limited understanding of your profession Hope it was helpful - and the "no one cares"  and "why should I care" are just standard essay points to keep in mind. Keeps things from getting too tedious/boring/etc for the reader. I'm sure in reality your life is quite fascinating but these people read tons of essays.

One prof in my undergrad was the main go-to for academics - that being because my degree is in theater, thus the profs are mostly art/design/etc.. focused - so he got the bulk of reccomendation requests.
 
He asked those he was willing to write a letter for to provide a summar of accomplishments, notable work he would have seen, and goals, etc.. to be worked into his letter. This seems totally reasonable.
 
Having you write it..? Pretty awful.. if you can find someone with a general interest in you for any other reason - go for that one instead. If anything, because it's a letter and that's just a hurdle and NOT a defining part of who you are - heck, he's willing to sign off on whatever you write - have a friend write it for you and then give it to him. That way you'll avoid your distinct "voice" from showing up in your on reccomendation.
 
Also, sometimes they have questions.. and will call. I was in my prof's office once when they called to ask something about me. Awkward to say the least. Luckily for me, I had been honest with my involvement in the project - long story short they called because they questioned if I had actually done what I said I did for a particular show in my portfolio because it was something out of the norm for a student at the undergrad level.