Wow excellent info Mabuk dan gila! Thank you for sharing your research and personal experience!

Since I am in the group of mid-20s with short credit history (~6 years on oldest card), I'll definitely try to play a bit safe. I've had many inquiries while shopping for balance transfer cards and also mortgages in the past 2 years, so I'm going to only do minimal card openings until many of those clear off over the next year. Based on your research, this should also be good for me to ensure my average age doesn't drop too low with too many cards opened in one year.

And based on your info, it sounds like assuming one doesn't have ANY outstanding revolving debt, there's NO damage in closing credit cards, since they still count towards age?