I have mine done like that every couple years (in addition to occasionally vacuuming it out and wiping down the dash myself). They get the crumbs and dust out of all the hard-to-reach places, clean everything, vacuum, and shampoo the carpets. Leather treatment is usually extra.
It's not about the age of the car, it's about how much time you spend in it. I'd do it on a ten year old car as happily as I'd do it in a brand new one, but I live in my car 2-3 hours a day.
It's time intensive and the detailing services I've used have some sorta-specialized tools (fancy vacuum attachments, weird little brushes, etc.), but it's not "skilled" labor (mostly 20-something kids making ~$12/hour, no specialized training except for on-the-job stuff.)
You can totally do it yourself; whether or not you should just depends on how you value your time and what other obligations you have. Same old story.