I'm about 160cm tall
With DD I started at 54kg, didn't start showing (at all!) until 27 weeks!!! So annoying having to wait that long LOL. I ended up putting on 12kg in total.
With DS I was over-weight when I fell PG. Started at 69kg, started showing around 10 weeks I think it was. Over-all I put on 9kg but in first tri I lost 6kg so I put the 6kg back on plus 3kg ontop.

I dont think it has to do with weight, I think its just pot luck as everybodies different. But reading the posts in here I'd have to say 4 months looks like the average

Congrats on your pregnancy... you'll have that baby bump before you know it! Enjoy