Inquiries will lower your score, but its a very very small dip. As for credit age, I've had an Amex for over 20 years and a couple of other cards open for a decade so they bring the average up and I close the new cards once I hit the sign up bonus so they dont effect the age of accouts once they are closed, so a couple of new accounts vs vs 4-5 old accounts balances out well. I dont think Ive ever dipped below 790 even when churning a lot of cards in a single year. If you have no late payments and low usage your credit will be great. Carrying balances on a bunch of cards is not good for your credit though.