<human>: Summarize the given text in a few sentences.

Hi there! I hope this is a simple answer, but the question has multiple components, so let's begin: 

-I am 23 years old and I have had a personal credit card since I was 18. 
-I have excellent credit, high 700s. 
-I pulled my credit report 2 weeks ago and everything is in order (no old unused accounts, always pay on time, etc). 
-I currently have 3 credit cards: (1) A copy of my parents Capital One Mastercard which has my name on it. (2) My own AmEx Premier Rewards Gold card (with a $175 annual fee), and (2) A Capital One Cash Visa (no annual fee). 

Until recently I was using solely the AmEx. However, I realized after a few months of heavy spending that the Membership Rewards program SUCKS. I'm not traveling at my age and I don't spend 10's of 1000's a month. I wanted to cancel the card and switch to primarily using the Capital One which has a flat 1.5% cash back (compared to AmEx's equivalent cash back rate of like 0.5%).

Here's the issue: When I checked my credit score, the tool said despite my good credit, I have low credit history. Additionally, my score was higher because I use a small percentage of my credit line (the AMEX has no limit and is calculated at 30K; the Capital One is only 3K). The AMEX is about 4 years older than the CO, making it my oldest credit account. 

So the question is: is it worth getting better cash rewards and saving the annual fee by canceling the AMEX and using the CO exclusively, or will the cancellation of a long time account PLUS lower overall monthly credit line affect my score negatively as not to be worth it?

(Side question: can I switch to another AMEX card and still maintain account "length" and without another "hard credit hit").
<bot>: Trying to avoid paying $175 a year for shitty AMEX reward card in the way that will LEAST affect my overall excellent credit score.