EDIT: I want to point out an important drawback of lying that people often overlook.
Each time you lie your mind will become more and more heavy because of burdens, this tremendously affect the quality of your life, as well as the high chance of rebirth in lower realm in next life, because a heavy mind will drag you down.
If you tell lies after lies, you have to remember which person you lied to, and the content of that lie, to stay consistent next time you meet them. And ordinary human being often have poor memory, and just a small slip can destroy your whole image, or even your life. Try to think about these burdens can be totally abandon if you always speak the truth and stay true to yourself, or in another word – integrity.
Scenario 1: You should avoid lying under any circumstance. In this case, how about just say “I don’t want to tell you about my personal things” or something similar. Having integrity is always better for us in the long run. In my personal experience, I always stay upright and being true to myself even at work, and my bosses know that and they won’t messing around with me. But If the worst thing happen then I just simply leave and find another job, any job that not violate Right Livelihood is good enough for me, I just need enough to sustain my body and my family. Having this attitude allow you to not be afraid under social pressure and give you energy to stay upright under harsh circumstances.
Scenario 2: In my case, I just simply say to them “I don’t drink”, as they ask me further, I just say “It’s personal reason”, and overtime, they gradually not focus on me any more. I think this is a good respond, you may not want to boasting about your precepts, but you also may not want to lie. If anyone really interested in the reason why I don’t drink then it is a opportunity for me to introduce them about the benefits of five precepts.
Scenario 3: I often tell them about my earning if asked, but if you don’t want to tell just say so, there is no need to wiggling around, this is also for practicing integrity.
Scenario 4: Again, just say what is true, or if you don’t want to say just remain silent or say “I don’t want to tell you about this information.”
Scenario 5: I’m a web developer, I don’t recall having seen any case in which your DoB on a online forum be used against you. But I also recommend hiding your DoB on social media platforms because hackers may exploits your information to build a dictionary and then brute-force your password if they desire. But I guess we are not celebrity so this problem is not really a problem. So my advice is just stay true to ourselves, we need every opportunity to practice truthfulness and from the very small things such as these, we build up our integrity.
The precepts need to be kept spotless and stainless, without any excuses if you want to proceed further on the Path. In many suttas the Buddha teaches about the qualities of a Stream-enterer (Sotapanna), one of them is spotless ethical conduct, praised by the wises.
Furthermore, having integrity is essential to even starting to walk the Path, the Buddha advised his son to not tell lies even just for a joke, you can see the seriousness in always staying truthful.
But to have a degree of faith enough to undertake the practice of integrity, you need to first learn about the Buddha’s teachings, develop Right View and gradually apply the Dhamma into your daily life. One of the most important views is the view about rebirth and kamma, you should contemplate on this, to leave no crack/hold for the tendencies to make excuses sneak through.