50 years is at the half century mark and who wouldn’t be happy celebrating such as fete? You should have more reason to celebrate your 50th birthday and if you have someone just about to do so, you should make it even more special for the person with a beautiful birthday card accompanied with a perfect phrase. Make special too by wanting to celebrate all the victories, successes and achievements in all those years.
You could use some witty 50th birthday phrases that say something positive about the age of the person. For instance, you could joke about how the person looks younger or how better he/she is getting with age. There is nothing wrong with using a humorous phrase and a funny poem or joke will come in handy.

For a 50th birthday invitation phrase, you just have to show how proud you are for getting to half a century mark and give people a reason why they should join you in this joyous occasion. Put a funny joke, quote or poem as part of the phrase and include any other things you may want to do during your special birthday but do not make the phrase too long.