Your AAoA will actually fall by getting new cards right now. I certainly would not recommend just going and applying for "as many" cards in hopes of boosting your scores.
In hopes of raising your scores I would start with looking at your utilization on the cards you have. You only want to let 1 card report each month under 9% of your total credit between all of your cards. Let the others report a zero balance.
Then, you mentioned not having any installment loans, and while I'm not for getting one "just because," not having one is losing you points due to the lack of credit mix in that category. You can look into getting a small secured loan. Search the threads on this topic for more info.
Last, you didn't mention it, but do you have any negatives reporting?
In hopes of raising your scores I would start with looking at your utilization on the cards you have. You only want to let 1 card report each month under 9% of your total credit between all of your cards. Let the others report a zero balance.
Then, you mentioned not having any installment loans, and while I'm not for getting one "just because," not having one is losing you points due to the lack of credit mix in that category. You can look into getting a small secured loan. Search the threads on this topic for more info.
Last, you didn't mention it, but do you have any negatives reporting?
Applying make sense if you're looking rewards you don't already have, or planning on a very big purchase (could get bonus cash), or rebuilding credit, etc. Would other cards do something for you that you current ones don't? You already have a good collection - there's not much more for your score that 8 or 10 can do versus your 6, if you're not seeking higher limits/lower utilization.
I think I'll get a secured loan then with a cu. Smallest amount and shortest term possible should be enough right?
The big positive impact of installments is that they are over a long term, like 5 yr auto or 15 yr mortgage, so lenders see that you can sustain those type of payments over a long period. Getting a small *unneeded loan over, say 1 year, wouldn't really help. You'll take the score hit from getting it, then a hit when you close it, and the duration of account would be very short (this is part of the age of accounts factor). Credit mix is such a small percentage of the score - why not leave it for when you actually take out a loan you need in the future?
It is a good idea to research credit cards, see if there's one or some that fits your current spending best, and if there is, you could definitely apply for them now to let them grow and age with the ones you have 
My history is like yours, with some different cards - I feel the urge to do *something* to improve my scores, especially as I read about card apps and score strategies on this forum. But I've realized the best option for me now is to wait, keep paying on time and have low utilization. When I travel more, I will find a travel rewards card that suits me. If my spending increases substantially, I'll see if other rewards cards are better.
It's nice to find a fellow credit sapling! Many members seem to have long histories and/or thick files.
@jesseh wrote:Nope, don't have any negatives. My report is literally just the cards in my sig.
I don't care about my score on the short term that much, so taking some hits now if that improves my score in the long term is fine with me
Sometimes i let no or multiple cards report a balance, which makes the score go under 750, but if I only let one card report the next month it's back at 760 or so again. As util of only the current month is considered in fico that shouldn't matter in the long term anyway.
I think I'll get a secured loan then with a cu. Smallest amount and shortest term possible should be enough right?
and do you recommend to apply for cards as I can take the hits?
A small secured loan can help your credit mix. You can do a small amount but a short term isn't the best way to do it.
I got my secured loan from my CU in January. They took the money from my share savings account for collateral. They lent me the same amount and immediately deposited it in my checking account. The loan term is for one year. I paid down the balance to less than 9% in 2 months. I didn't set up auto-pay. I now pay them $5 per month.
Once I paid down the loan to under 9% I got the message on my reports that I have made substantial installment loan repayment. It gave me a 15-20 point increase.
Once the loan is paid off I expect to lose that benefit but I will have another installment loan by that time.
As to getting more cards; I am a firm believer is only getting the cards that will be a benefit to your personal financial makeup.
I enjoy spending time in the garden. My INQs age off and my AAoA rises. That doesn't mean I will stay there forever. I plan to join the PenFed family in October. Next year I want to buy a house. After I get the house I will app for a Lowes card. I like the low and slow approach.
