I assume your insurance will not pay because they feel ADD is outgrown after puberty. Ask them why and if this is the reason, write a letter of grievance to your insurance company regarding them to review the scientific literature, and petition the decision. If they still deny it, tell your physician about it and see if he can prescribe it via another diagnosis. i.e. depression.
Also if you've never taking ritalin before and you're not sure if this is the 'ideal' med for you, see if your insurance covers adderall. Also check the other chemical 'make-ups' of ritalin. Generic version, concerta, metadate, etc.
But if the brand-name ritalin works the best for you, then go ahead and file a petetion to your insurance company.