This is the reason I have just stopped bothering about privacy. I meticulously guard which apps I share my phonebook with, while other idiots share their entire contacts folder (including my details) en-masse to apps like TrueCaller.

It just feels so futile to even care.

You're right, facebook and others can (and do!) infer people based on contact lists, even if you don't have a facebook account, if all your friends do then Facebook already knows who you are, who your friends are, you're likely interests (based off friends), etc.

The best I figure I can do is to keep the apps I used locked down if possible - and to avoid "stupid" apps that clearly have little purpose other then dataharvesting.

Cool Selfy app? Ehh pass.

Didn't Facebook face tagging work the same for a long time? It would ask people to provide names for other people in their photos

Still does, at least partially. Facebook's always asking me if I want to tag certain people in their images... No Facebook, am no a grass

Can a friend agree to these terms when it is my face, my name, and my private data though?

Define private, you walk in public in front of security cameras wearing your face in public. your face is now public information.

Your name is on your mail, your census, your driving licence, you provide your name and address to companies all the time. your name and address is now public information.

If someone can tie your public face to your public name then thats public information.

you dont like it, get a PO box and wear a mask all the time.

In many countries including the US, yes. If the right mixture of you, the company, and your friend are located in or deal with Europe or similar places, possibly not, but it very much depends on the details.

Do friends need to enter the name along with the picture? How about the age?

I haven't tested the app myself yet and probably will not.

Same