How long can you keep a baby/toddler in a stage 0 carseat?

[CherryChoc]

DS is 9 months and weighs 8.86kg. His infant car seat (a basic Mothercare one) has a weight limit of 13kg so he is way off that. His head is not over the top of the car seat either. The problem is it doesn't feel very sturdy if I carry him in the seat using the carry handle. (I usually carry him and the seat into the car separately anyway.)

Basically I want to know, how long can I realistically do this for? Will it be safe as long as he is within the weight limit (which if he stays on the centile he's on won't be until he's nearly 2) and of course his head is not over the top of the seat? Or is there anything else to consider?

We have got a Group 0+1 seat which I will move him into when he outgrows his infant carrier but I want to keep using it as long as possible as I don't drive myself and this one is really easy to install and fits in every car I've tried it in. I just don't want to be using it if it's not safe IYSWIM. (Also would like to keep using this so I have the excuse of "Oh it's easier to install" because I think my mum will keep on to turn him around the minute I switch to the Group 0+1 seat, and also I will still be having lifts from friends who have similar aged babies and I don't want to come across as smug or preachy about rearfacing car seats.)

Hope this makes sense as it's quite late now

[OrangeFish]

If the head is not over the top of the seat, and he is in the adequate weight range. I can't see a reason to stop using it right now.

[thumbwitch]

My DS is 19mo. he is still around 10kg and therefore nowhere near the 13kg weight limit on the M&P travel system carseat that we have. We like it because it faces backwards.
His head is not above the level of the seat (although we did have to take the hood off because the hoop of the hood lies below the top of the seat when folded back).

Does that help?

[sheepgomeep]

I kept dd1 in 0+ until 17 months, and dd2 till 14 months

[ThePhantomPlopper]

DD is still in hers at 17mo.