You need to thoroughly read your documents. They should tell you exactly how the assn is to be managed. If there is only one assn the reserve fund should cover all the units, not just the older ones. Since your units are only 12 yrs old it's possible major repairs have not been needed so far. It's understandable that the older units would have more major repairs. In an HOA everyone pays for everything where they need it or not. In other words, you assessment is used for everything not just to maintain your units. The same with the assessments collected from the older units. That's just the way HOAs are run. 
 
You may want to take a good look at who is serving on the board of directors. If a majority of the members live in the older units they may not be acting in the best interests of the whole assn -- just worrying about the older units. Are the newer units being neglected? If this is the case, perhaps it's time for a change on the board. Instead of complaining try getting involved. In most cases only the board members know exactly what is going on. The members may "perceive" that something isn't quite right, but that doesn't mean it's so. Just a thought. 
 
And, "no" I doubt very seriously that you can just form your own assn. The only way that would be possible is if there were a master assn. Then each section (older and newer) would have their own assn but also be required to be a member of the master assn. The master assn would have gov docs that each section would have to adhere to and also levy assessments. 
 

Three words: Money, Lawyers, Accountants.  
 
The Association would have to be closed and immediately re-opened as two separate associations -- or a Master Association and two subsidiary new associations (one the older building, and two the newer.) 
 
But why would the Members of the existing Association vote to allow the division? It would cost them money and few of us (beside you and me) are that fair minded.

Here in Clearwater, Fl where I bought are two groups of condos' 55+. The first built was 1977 and association created as Villas I. Then the 2nd group was built in 1978. The 2nd units look as the 1st when built but at completion a 2nd Association created as Villas II. Villas II is the evil associatiion as they had rules Villas I allowed. Villas I doesn't want anything to do with Villas II. Just a brief history of Association dislike to each other. Then there are the 55+ private homes also with their own Association and all 'three' under the one HOA. 
 
So maybe advice from a Lawyer may check on rules on the newer units to become their own Association. It was done here so there must be a way to separate. I wouldn't give up the task. Even start with your state association that governs condos'. I wouldn't want my condo fee's being used for much older units. Doesn't sound fair or then you should be paying less towards the funds. 
 
Good Luck... 
 

Albert, 
 
 
 
What you describe is a master assn with each section also having their own assn. I'm thinking you pay assessments to both the master assn and your own assn and have gov docs from both that you must abide by. When the development was created it was determined that a master assn would be formed to control all the separate assn's in the development. This is not something that can be done years later. I doubt that the OP's units can just break away from there assn now and form there own.  
 
I think what everyone needs to understand is that the assessments collected are used to pay the expenses for all the units. The only inequity would be if the newer units are not being maintained properly because all the funds are going toward maintaining the older units. The OP did not say that, only that she didn't think it was right for the newer units to pay for maint on the older units. Sorry, but that's the way that HOAs are set up to operate. Everyone pays for everything whether it's something they use or not; in this case, whether it's for their unit or not.

You need to have a Reserve Study that includes all units. This will insure that your dues go toward saving for a new roof and other reserve expenses. 
 
A reserve study is now a standard part of financial planning for condominium associations, and is required by law in many states (often with mandatory disclosure to the state). I don't know if Tennesee requires it, but the board of directors and has a fiduciary responsibility to protect the association from financial hardship (that could easily occur without a plan). 
 
Establishing healthy reserves by implementing a reserve study will help to: assure that the costs of maintaining the property will be fairly shared by owners now and in the future; provide a predictable, manageable contribution plan; assure financial stability; enhance property values; avoid special assessments (extra owner contributions beyond the monthly fee); and provide a plan for maintenance needs. 
 
Does your association have a reserve study. If not, suggest it.

Your govern