Till what age (years) limit can a child sit in the pram?
There's no official limit, really. The general approximation is 3 years of age, BUT, like with car seats, it is more about the child size, weight, and, of course, needs. There are kids walking around 1.5years, not even wanting to see a stroller anymore (my firstborn was like that -_-), and also tiny children that are fitting even a reversible seat stroller at the age of 4, not strong enough to walk long distances.
Also, there are the special-needs children who, in general, use their stroller much longer than your average child - sometimes even their whole life, passing from a stroller to a wheelchair of sorts later on.
The reality of stroller days is that you should listen to the needs of yourself and your baby. If your child cannot walk too long and you need to do long walks every day, a stroller is a must until the child gets stronger. It can use a stroller until it fits inside ;-) If the child, on the other hand, wants to walk, let him/her, and perhaps have a travel stroller at hand, just for those few occasional uses.
And, to help to have at least a general idea, realistically, I know no mum with a healthy child still using a stroller after the age of approx. 5-5.5 years. So that would be my personal approximation of a limit, where, still, there is a relativity of needs versus the child's size and weight.