In the code specific details, there needs to be an "age limit" field - much like there is an "insurance payment frequency" field. Many procedures (fluoride, sealants, ortho, etc.) ARE available on plans, just not for adults. Our estimating would be much more accurate with this.
On a much more infrequent occurrence are those services where a patient has to have reached an age MINIMUM in order to receive a service (crowns, for example). This is far less necessary, but if you created an age block, and then we could check "minimum" or "maximum", that would take care of all the above scenarios.
But if only one can be done, I would use the age limit (MAX) for sure.