Well, there are a couple of things that stand out to me from your description. The first two other people have mentioned...
Excellent advice!! ITA!
To
@tryingto :
It's totally possible for you! I've never had hair longer than 3-4" since I was a child until I started my healthy hair journey. I lurked in long hair threads to see what those ladies were doing - I wanted to learn from those who had what I wanted. The common trend I saw was to keep it simple, low manipulation and maintain my protein/moisture balance. I have fine stands (4b) and extremely low vitamin D as well. it's more about technique than products.
PSing is key to retention- you just have to find the right PS for you.
From 2010-2013, I alternated, 3 weeks at a time, between mini braids and wigs. I found that mini twists caused my ends to knot severely.
In wigs, I finger detangled and cornrow braided my hair on Saturday, washed and DC (light protein and moisture) on Sunday in those cornrows and then water rinse or cowash daily. I kept those same cornrows in until I redid them the next Saturday, one by one. I also kept my hair covered when I was home to prevent HIH and friction. I rarely used heat and rarely used a comb. Fine strands need low manipulation.
In mini braids, I just cowash or water rinse daily and do my weekly wash and DC (protein and moisture). I also covered those when I was home.
In essence, I kept my hair stretched in some form of braids 95% of the time and rarely messed with it. M&Sing my hair at night helped to keep it moisturized in conjunction with the cowash/water in the morning shower.
You can look at my album (I think) and see that I retained a lot using that low manipulation regi. I went from shaved head to APL in a short time. You can do it! Take Raven's advice: stop the cuts and track your progress using a shirt.
Regarding trims, I only believe in dusting and I did it once or twice per year. These days, I only dust once per year.
Here's my progress, if you're interested. BTW, I'm closing in on 40 so youth definitely did not play a factor in my progress. Lol.
June 2009
April 2011 (using my makeshift length check shirt)
April 2013