Student or Learner
a. How come you look so young at the age of 50?
b. Why do you look so young at the age of 50?
1. Are the above sentences correct in grammer?
2. Are the above sentences the same in terms of meanings?
3. Is how come more causal in coversation that we should not use it causally but only to the closed friends?
4. What are the differences between in terms of and based on?
Can I rewrite the question 2 to :
Are the above sentences are the same based on the meanings?
Your first two sentences are correct but we wouldn't say that. It sounds a little rude. You can say "You look great! And so young! What's your secret?" or "How do you manage to look so young?!" or something like that...