Sorry to burst your bubble mate. 25-30 is normal for healthy cockatiels. Trouble is that most of them die well before their time is up because of un(mis)diagnosed illness.
Think about it.... When you go to the doctor they just take an educated guess at your ailment and usually confirm this with tests. When they get it wrong - which is more often than people realise - they just go on with 'we'll try something else'.
A cockatiel can't tell the vet where it hurts, how it feels etc. and seeing you get 10 to one kilogram, there is not a lot of body mass to fall back on. Usually when you notice a bird is sick, it is too late.
All this doesn't alter the fact that you've obviously taken good care of your 'tiel and don't be surprised if it lasts another 10 years or so.