I think gender and birthdate are important information for selecting a suitable partner. For example, I prefer to speak to females around my age, rather than males or females who are much younger or older, as I find it more interesting to chat to them. It doesn't ask for your address, just your country and city (I'm pretty sure city is optional), again information that is often useful when picking an exchange partner (for example, the Spanish spoken in Spain has certain differences to that spoken in Mexico - usage, accent, slang etc).
I didn't realise Bussu showed ads since I use Adblock but I agree that the ad they are showing you would be annoying.