Thus speaks the terribly experienced Mum of one.
I've got three. They are and were all different in lots of things, including sleep and routines.
Dd1 slept through, 12 hours in the night (8.30pm-8.30am) 3 hours in the afternoon from about 6 weeks old. She fell naturally into a routine and all was easy. She dropped her afternoon nap only just before going to school at nearly 5yo. So clearly I did everything right.
However dd2, who I did exactly the same with. She didn't sleep more than 2 hours until she was 20 months (when the doctor gave me the wonderful, but discontinued "Medised"). She also had a scream like a banshee, and went 0-60 in about 3 seconds upon waking, so would wake the neighbourhood up. Luckily the neighbourhood was generally very nice about it. She would dose for about 40 minutes in the afternoon, but didn't settle in the evening until around 10pm, and then wake for the day sometime between 4 and 6am. She was far worse with routines - she resisted them and got unsettled.
I can assure you I tried almost everything to get her to sleep.
Ds' sleep was immediately different. In length (barring ear infections that happened regularly) his sleep was more like dd1's thankfully. However the timing was totally different. He started wanting to be put down for the night about 5pm. I'd desperately try and keep him awake a little longer and eventually put him down about 7pm.
He'd wake for the day about 6am, and then he'd have a couple of hours morning nap.
As adults, you can see this still in them.
Dd1 is a night owl, who likes her sleep. She'll often be up beyond midnight, but needs her 8 hours sleep. She prefers to have a lie in, but if she knows she won't get one will go to bed earlier. She likes her routines, and tends to do the same things before bed.
Dd2 burns the candle at both ends. She'll sometimes be still up at 2am, but then gets up no problem at 7am when she needs to, although she won't get up early unless she has to. She's not into routine - it's what she fancies on the day. She does now have lie ins when she can, although that might involve more reading than sleeping.
Ds still is a morning person. He's often up and working at 6am. If he's still in bed after 9am I know he's ill. He'll not usually be still up at midnight unless he's busy. He was and is a stickler for absolute routine - even if he is really ill and struggling to stand he'll still do what is his routine.
Even babies have their own preferences and personalities.