Go ahead and apply for the job! Do not mention the vacation until after you have secured a new position; I can't tell you how common this is. Several friends of mine had big trips planned for times within a couple of months after starting a new job. They told their new employers after the offer was accepted and they all went on their trips, some though, without pay, which was fine.
Yes, there is ageism, but it depends what field you are in. I will be looking for a job in May, when I graduate, at age 57, but thankfully, age is seen as a plus in counseling and quite a few people in my new field make me look like a techno-expert, which is a laugh.
If there are jobs in your field, go for it. My son , who is 28, just started a new job at the end of August. He had been looking for a year. He had a job, but he knew it was time to change. He went on several interviews, did some volunteer writing that enhanced his resume, and networked like crazy. He got his job from someone who contacted him on Linked In. It was definitely worth the time and effort. Keep positive. There *are* jobs out there... the people I know who graduated in my program last spring all found jobs.