Is that 50-55% estimate conditional on no civilizational collapse or extinction event? Either way, it seems very optimistic. According to current actuarial estimates, a 30 year-old has about a 50% chance of living another 50 years. For life expectancy to dramatically increase, a lot of things have to fall into place over the next half-century. If you think anti-aging tech will be available in 30 years, consider how medicine has advanced in the past 30. Unless there are significant breakthroughs, we're sunk. I'm signed up for cryo and I donate to SENS, but my estimates are much more pessimistic than yours.
I believe I used a fairly small number for civilizational collapse and extinction, on the order of ten to fifteen percent. I just don't find such doomsday scenarios that likely or plausible.
It may be that my background and upbringing have inured me to it - I've seen the end of the world not happen far too many times in my lifetime:
I wrote an article about the process of signing up for cryo since I couldn't find any such accounts online. If you have questions about the sign-up process, just ask.
A few months ago, I signed up for Alcor's brain-only cryopreservation. The entire process took me 11 weeks from the day I started till the day I received my medical bracelet (the thing that’ll let paramedics know that your dead body should be handled by Alcor). I paid them $90 for the application fee. From now on, every year I’ll pay $530 for Alcor membership fees, and also pay $275 for my separately purchased life insurance.
http://specterdefied.blogspot.com/2015/04/how-to-sign-up-for-alcor-cryo.html