My eldest was 2 years and 4 months when his little brother was born and 19 months later we're still using our double! Our boys are now almost 4 years old and 19 months, we have a City Select. You can use it as a single pram too so quite often DS1 will walk or sit on the front bar if you can imagine what I mean, but there are some days where he doesn't want to walk so we pop the 2nd seat on, great for big days out at the zoo or something as well.

I wouldn't be without our double!