What's your background?
The age thing wouldn't be a huge deal, if you had a BA and/or MA already. This is more the problem:
>are any students admitted without previous academic philosophy training?
Anyone can apply to most programs, even (I think) people with very unorthodox backgrounds, or no academic background at all. But the vast majority of people who get into any good program (more on program quality in a second) are going to be people with predictable backgrounds. It's not unusual for a philosophically inclined person to have a Bachelor's in some field like Anthropology or History, but most are going to be Philosophy BAs who then do a Philosophy PhD.
The reason for this is simple: Graduate programs are looking for applicants who are likely to succeed. If they see someone with a BA in Philosophy, and a high GPA in it, they know instantly that he's not a total fuckup. They know that he knows at least something about what academic Philosophy is, and what is expected of him if they accept him. If they see someone applying who did their BA in Literature, they'll still be open to it, but they'll double-check to make sure the person meets those same qualifications. If he has zero philosophical background evident in the courses he took in undergrad, his statement of why he's applying had better clear that up and make damn clear that he knows what he's doing.
Theoretically, the same could be said for a total unknown. I'm sure if you published some magnum opus at 20, as a total nobody who worked at a laundromat, became world famous, and then applied to Harvard, they'd be interested. But:
a) Almost all of the time, they're just going to assume that applicants without relevant backgrounds are naive and don't know what they're doing, and that it's just some random guy who thinks he likes philosophy.
b) Almost all of the time, sadly, they'd probably be right.
A lot of doing academic work is just being familiar with what the academy is doing, and having been trained to look like you could do it. If a modern day Nietzsche, working at a laundromat, applied to a top tier Philosophy program, they'd probably reject him and admit some boring, middle-of-the-road, derivative dipshit who has a nice safe 4.0, because it's not really their job to take risks. And most of them are derivative specialist hacks as well.
>does anyone get a fellowship/scholarship to do a phd?
Usually, you don't go unless you get funded. Getting a PhD is years of taking classes, reading, writing, and jumping through hoops, so you need financial support, and obviously to have the ridiculous tuition waived.
>program quality
One of the other problems is that academia kind of sucks right now. It's bloated. If you want to have a career, you will probably want to get into a relatively exclusive program.. But the more exclusive, the more they will be looking for those picture-perfect Princeton graduates.