DD spoke in sentences very early, and has always used quite "adult" words for things (which we generally thoguht was due to her being the first and still an only, and in the company of lots of adults, as well as us refusing to do "babytalk" - although she went to creche with lots of kids too from 3 months old).
Could be fussy about food, and clothes. Still lives in tracksuits if given a preference, and it's ridiculously hard to get her into a dress or skirt for formal occasions.
Routine was and is HUGE. If we say we'll do something, we have to do it. And she takes things very literally as well.
She dropped her daytime naps very early - she was awake all day in creche when still in the toddler room (moved to montessori aged 2yr9mths), and while she then took a 15 min snooze while she got used to that, she was back to not sleeping within a couple of months again (when lots of the 4 year olds were still having an hour sleep after dinner).
She also seemed very advanced academically. She flew at things even before moving into montis (the toddler minder was monti trained so used to get a few of them doing things before moving) - especially maths-y stuff.
But close friendships were not really there. She was friends with everyone there (small class of 8), but not really bothered not seeing them once she left (school close to home, creche was close to work). She has one close friend - they kill each other as much as love each other (mainly verbally, but the buddy can lash out, at least DD has learned not to do that anymore, or much more rarely).
She can get very aggressive - usually with DH and I rather than strangers or people she would see less often. So only with those she is very comfortable and secure with. And we've recently realised that what we took as being shy with strangers (which could include family members too), was more anxiousness and being scared. But once she was in company with someone non-threatening for a while (like grandparents), she would relax and start to chat away with them. She's not the most touchy-feely person either, and tends to run away from hugs and kisses (which most family cannot accept).
But she's also very funny, very logical, very loving in her own way. Wants to help and get involved. Will do a lot once she is shown how. Just make sure that you leave "her" jobs for her to do (she has whipped eggs for baking since she was under a year - and I am not now allowed to do them unless I am baking in the late hours and she's in bed, when I might still have a whinge the next morning).
She's now 6yrs5mths, and we got the high functioning ADHD/Aspergers Dx a couple of months ago.
Sorry, that wasn't meant to be an essay. I just tend to keep going once I start.