Don't worry, you won't be the only single man when you're old. Also, at what age would you define "old?" There are men over 40, 50 and 60 who have great times at the bars and even meet people on RealJock. They live active lives even though they are single and they hang out with their friends and have a good time. There are single men on this site who are well into their 50s and they don't seem to mind.
Finding a good relationship is not a race in which, once you reach a certain age, the whole world will end if you're still single. Are you enjoying your life right now at 28yo? If so, when you were a teenager, you probably thought that if you were single by the time you turned 28, that life would be hell. Well? Is life hell for you at 28? If you say "no," then what makes you think being single at an advanced age will be bad and that you need a backup plan? When you're over 40 and still single, just keep enjoying your life with your friends and other activities like you always have. Your "backup plan" will be living life to the fullest.