I have 4.5 year age gap between mine and its perfect.
Before ds2 came along I thought that there were pros and cons of having either a bigger or a smaller age gap.
Ironically, I figured if they were close together they would get on well. When I see my friends who have two close in age, I realise that I was wrong. Very very wrong. They have always had to compete, I realise there will be some close in age kids that are great friends when they are little but I haven't yet seen it.
Mine have always got on amazingly, by the time the baby came along ds1 was old enough to understand, to empathise to my tiredness, for me to explain that I could help him in 10 mins while I finished the baby's feed, or old enough for me to leave down stairs safely while an spent 20mins settling be baby to sleep up stairs. None of this happens as easily with a 19 month old running around.
They get on like a house on fire, they adore one another. They can't wait until the youngest starts school (in September) so they can hang out with one another, they giggle together, play together, want to share a bed together (!!) and miss one another when ones at school.
I always thought the novelty would wear off but 3.5 years on they are still close.
Now, I can't see any cons of a 4.5 year age gap, I can only see great big fat lovely pros.