What is the ideal age to get a PhD? There have been a few "how old is too old to get a PhD" questions, and I don't intend this to be a duplicate--they were more focused on age from an actual admissions standpoint.

While I'm interested in general to hear people's thoughts on the question I posed, I'll also give my own current situation, in case anyone has thoughts here:

I'm currently 25, 2.5 years out of undergrad. I got my MS degree directly after undergrad, which took 1 calendar year/3 semesters. So I've been at my current job at a research org for 1.5 years now. My current plan is to apply for my PhD at 27, so I'd be starting at 28. I think this is the ideal amount of time to improve both my skills and my CV, but isn't too long that I will be middle-aged when I finish and have a more difficult life adjustment as a PhD student, and have less time in my post-PhD career. If it makes a difference, I'm in the social sciences/public policy field. 

Thoughts? Am I dumb to wait until my late 20s? Should people all be waiting until they're 30 because they're too young and unexperienced out of undergrad? Is it undergrad-PhD straight through or bust?
There is, frankly, no "ideal" age for starting a Ph.D. There's not even a "better" time. All that is really important is demonstrating that you have an aptitude for doing research in the proposed field of study. If you can demonstrate that at age 20, great; if you've had a change of heart at 30 or even 40, and decide you want to go back to school, that's cool, too.

However, there is an advantage in doing it sooner rather than later—adjusting back to "student" habits is easier when you're closer to finishing your undergraduate than when you're older. It's also usually easier to move around when you're younger than when you're older and might have a (larger) family to worry about.

But from the perspective of someone who reviews admissions applications, I'd say the single most important factor is demonstrating your potential to be a PhD level researcher. If you can do that, I'm not nearly as concerned about someone having a 3.4 versus a 3.6 or a 3.8 GPA, or a 155 or a 165 on the GRE.