I have also carried my toddler in a ring sling till he was at least 2, and still do it sometimes now that he is approaching 3. It's just that it's not comfortable to carry a heavier baby/child in a one-shouldered sling for long periods. It depends on your plans for carrying your baby. If you're anticipating shopping trips of 2 hours with the baby on your hip, then my opinion is, it's not that comfortable!
However, if you want the sling for settling at home, doing housework, short walks to the supermarket, getting in and out of public transport etc etc, then they are fantastic, very easy and light, and convenient.
In fact I'm taking the sling with me on an outing tomorrow so that I can leave the stroller at home. For those times when my 17kg nearly 3 year old wants to be carried, I'd much rather do it in a sling than just with my arms!