Hi I'm new here and I'm extremely happy that I found this thread since it is what I was looking for.
I'm 22 years old and I've been counting letters since I was 14...I think, as that's as far back as I can remember doing it.
It takes me about 3 seconds to count the letters in a sentence involving 5-10 words of medium complexity. I then go on to add in other words into the sentence to make it equal a total number that ends in 5 or 0. Then I take the first word of the sentence and put it at the end, and move it in between each syllable until it gets to the front, then i go front to end, front to end, and end to front. The whole time I do this I alternate inhaling and exhaling with each syllable, making sure I end on an exhale. So i.e. let's use the sentence "What are you talking about?" for a total of 22 letters.
I would insert "And" into the beginning of the sentence, making it "And what are you talking about?" for a total of 25 letters.
Then I would read it in my head as "What are you talking about and?"- "What are you talking and about?"---"What are you talkanding about?" and so on and so forth.
So far this hasn't caused much trouble in my life, it's more of a minor annoyance.