Carl Powers case 1989 when Sherlock was "a kid", but you also need to think about the fact that Moriarty killed Carl Powers using botulinum. I've never really placed Moriarty as being that much older than Sherlock, and for him to have a decent enough knowledge of poisons to know how to kill someone, he would need to be at least 12 I'd say...

This is why I place Sherlock at 13 years old at the time of the Carl Powers case, and I have him born in 1976 which is the same year as Benedict anyway so makes sense. This would make him 34 when he first meets John.

John is always supposed to be older but not by that much. I put him at 4 years older, so 38 when they first meet.

Mycroft 7 years older so that would make him 41 at the start of Series 1.

Irene...Sherlock mentioned that she was born in the 80s and she didn't contradict him so we can assume he's right about that (as he's right about most things anyway). I was born in 1986 which makes me 26 years old now, but I've always imagined Irene to be older than me, born in 1982 which would make her 30 at the time of Series 2.

 

Well, it wouldn't change my John/Sherlock/Mycroft ages, as I've also worked that out based on January 2010, but I had my Irene age calculated based on it being 2012 when they dealt with her case. So if I was going off your dates, that would make her 29 when she meets Sherlock. That still works for me.
 

Yeah, I know what you mean. I think that's why I made the timeline a bit longer than you did, because a lot of time passes during that case alone. Christmas, New Year etc, and then Sherlock's road trip to go and save Irene, which must have taken a good few weeks out of his schedule.

Hmm....I'm going to study the casebook again and make my own timeline I think.