I kind of hate it when people claim people who have a nice experience are lying.
"You're slim? You have an eating disorder and you're LYING!"
"Loving marriage? You're LYING!"
"Cook your meals? LYING!"
Can't anyone have a bad time of something without accusing those not suffering it of lying?
Right. Look. Kids are all different. Some sleep, some eat, some do neither. My son adored my daughter on sight. He stroked her tiny hands and gazed into her eyes during nappy changes, he joined her on the blanket for tummy time, he abandoned all his games when she was awake to hold toys up in front of her and talk to her non-stop. When she got older, he was her favourite person; she'd crawl to him, he'd hold her hands, teach her games. Never once showed impatience. Found everything she did impossibly delightful. Now he's 8, she's 4.5 and they're just the same. Hold hands all the time. He gives her a big hug and kiss on the top of the head before school, in front of his friends. He's even been known to write her name on his schoolbooks - very small, under his own - because he likes to think of them as a pair. They never fight. They rarely play apart.
Nothing I did. Nothing anyone did. It's just the way of it. My son won't eat greens. They claim to 'hate' sports. My daughter won't let me do plaits in her hair. Eh. We all win some and lose some.
I think the age gap does make some difference. Teeny tiny kids don't even notice the sibling, they're too small. Older kids notice it but don't see it as a threat, because they are secure in who they are, they can appreciate the baby is very different to them, and don't feel so threatened by its presence. They also have school to distract them and have baby-free time. Between those ages you have a more ego-centric kid who still feels they're the centre of the universe and doesn't want to share. Give them a bit of one-on-one time, but ultimately, it's one of life's lessons they need to learn.
There'll come a time they don't even remember their life pre-sibling. My son was almost 4 and he doesn't, even though he can remember certain events - he just assumes his sister was there.
They get over it.