This was a question I tried answering myself while I first watched the series, using cross-episodic evidence. It's interesting to see a thread pop up about it.
One thing I'm sure of is this -
Mako's exact age: 22 or 23.
The math is simple. Kaoru is 17. Let's assume that the previous battle with Doukoku at the mansion happens in the year before Kaoru was born, that makes it 18 years before the 18th/19th generation of Shinkengers reassemble. In Act 34, Ryuunosuke notes that Mako was only five after that battle. So that makes her 18 + 5 = 23. If it happened in the same year as Kaoru's birth, Mako is one year younger 22.
Ok I MUST make this clear. Takeru is no teenager. He's not 19, an idea that was raised earlier. Given this same 17 or 18 year gap, in order for Takeru to be 19, he had to be just a one year old toddler when his father gave him the Shishi Origami. That's not what happens on the show. To decide if Takeru is older than Mako or not, we'll have to ask this: Is the young Takeru from Act 46 older or is the young Mako from Act 34 older? I think they're the same age, or maybe she's younger than him.
Comparing Mako with Ryuunosuke - I don't know why, but he just doesn't seem as much as an adult as she does. She's already thinking of Mr Right and he can't even get over giving up Kabuki temporarily. And here's the more crude point. He is revealed to have both a mother and father complex after all...
Read this section only if you want the explanation for why Mako has to treat Takeru like a kid more than anyone else, and why she doesn't really get involved in Ryuunosuke's life. I've left it concealed as a "spoiler" for Literature lovers (like me).
Mako talks about marriage, about settling down in life but rejects Ryuunosuke at the end of Act 4. She's steady, and is prepared to move into the next part of life (once her cooking improves haha) and all. Her care for people doesn't really seem like something to do with age. It's more likely that she can relate to people who still have a childlike side to themselves. Takeru really is a grown up kid - he spent his life on swordsmanship. He's not actually grown up as Takeru. He's still the boy from 18 years ago, now with an adult body and improved sword skills, and he's had a tougher life than the previous ShinkenRed's as he actually has the responsibility of being a Kagemusha, something not even the other Shiba Lords had to handle. Jii knows this very well. Ryuunosuke reveals his kid side whenever he hides in Takeru's shadow and when he talks about his past with Kabuki theatre. Chiaki and Kotoha ARE technically the kids in the Shiba household. Genta is a Shinkenger because he clung onto the childhood promise - and that clown from Takeru's childhood still remains by the end of the show. All of them had their "distractions", Takeru has a responsibility, Ryuunosuke has Kabuki, Chiaki and Kotoha have the father and sister respectively and Genta has sushi. Only Mako had nothing. No adults, (except her grandmother for a while) and no distraction from the bad past. So she kind of makes herself her own adult guardian after the grandmother leaves and that's why she bothers about the other five, because she feels she has to be the adult guardian of these people because she never had one after her Samurai training was done. This is also a reason why she works at the childcare centre. Of these five other Shinkengers, Ryuunosuke hides that child side very well, much better than Takeru himself. He even resolves everything by promising to return to Kabuki after sealing Doukoku in Act 35. He doesn't need to be watched over like a kid as much. Takeru's child within is too obvious to hide. So she has to watch out for him first.
Genta as a boy appears to be older than Takeru and the young Ryuunosuke who appears in his flashback in Act 4 if you ask me. So if you ask me it's like this:
From oldest to youngest,
1) Genta
2) Takeru
3) Mako
4) Ryuunosuke
5) Chiaki
6) Kotoha
I think I've been able to substantiate my ideas to some small extent, and of course I might be partially wrong, but this is the best possible age analysis I could do for Shinkenger as a Literature student.