From what I heard Emirates are not strict about how high you are but are you able to perform work, so if you are good performer and well presentable you don't need to worry about this issue.
You said that you are overweighted and as far as I know, I saw lots of theirs crew and they all seemed normal weighted. However my personal advice it's to find EK cabin crews pictures or videos on the internet just to have some image in your head and if possible get thiner. About age issue, yes I have heard that they do recruit people over 30s.
About your online application you shouldn't expecting to hear from them,I attended OD with EK two times first time received an invitation,second not. OD it's walk in day and anyone can come no matter he received an invitation or not. I am not sure I did understand about the agency, but if you want to find next OD date in your country try on emirates site or
www.cabincrew.com.
Good luck!!!