This site is all about supporting people and sharing our experiences with others. I have never been one for upbeat comments as a means of support because most people on here could hear reassuring comments without having to come to the site. Anyone they would share their story with could say things like, "It will get better." or "He'll realise his mistake." when the reality is it may not and he probably won't.
In my experience, being in relationships (I'm 51, divorced twice, serial monogamist) is a chance we take. There are no guarantees. Relationships end for lots of reasons and sometimes we never learn the true reason. According to the ABS, in 2013 there were roughly 119000 marriages in Australia and 47000 divorces. Divorce is a shade under 40% of marriages and the figure is stable according to the ABS.
It is not right for you to blame yourself for any one of the many reasons your relationships ended. The end of a relationship does not mean you are a failure or did something wrong. Many men (and increasingly women) are being drawn to much younger partners these days. Men have often been suckers for younger women but look at the explosion of the modern "cougar"!
Please do not blame age, it might be a distraction but very few relationships that are long term have age disparities. Sure, we all know a couple or two that have a lot of years difference, but most of the couples we know are within a few or five years difference.
I hope you can reconsider the reasons those relationships are over and not see yourself, or more importantly, your age, as the causes. It is not easy but it is true, I think, that you must prioritise yourself to attract the right person. If you do not think you are a good person, that you are not worthwhile, why would you think someone else would?
Can I please ask you to post some more or contact the 1300 number on here? Alternately, discuss how you feel with your GP.
I'll look out for your posts. Kind regards, John.