Look, a larger world with the same rotational speed will have more "time" in a day.  Even if they can divide it all evenly into 24 hours of 60 mins of 50 seconds each, those seconds would be longer.  Then again, they could be shorter.

Some can go for the orbit of the planet around its sun.  Years can be longer or shorter.

The variables you suggest are more variable than you want to comprehend.  The measurement of time is subjective.

18 years of Terran time is measured by 18 rotations around Sol. Which is not the same as 18 years of Martian time, which holds a different orbit:
A one year old Martian would be different from a one year old Terran...  And we know nothing about Carna, but I will point out that probability tells us that it is extremely unlikely that Carna will have exactly the same orbit around its sun as our planet does ours.

No the variables as I have given them are simple.  I have stated birth is at "X" (I NEVER said that "X" had anything to do with the orbits or rotational speed).  The verbage used to describe "X" can (and probably does) vary from culture to culture and planet to planet.  None of which changes the fact that "X" is a fixed point in time.  With today described as "Y", the AGE is the difference between "X" and "Y".  If you want to measure that difference in days, hours, centons, rells, or any other word we may have come across as being used doesn't change what the difference is.

If you want to argue that 5 Aleran years are longer/shorter than 5 Terran years, please find me some book evidence to support this.  Otherwise I would say it's "Occam Time".  The simplest answer is that the length of a "Year" there is roughly the same as it is here unless there is quality evidence to the contrary, and I do not think we have been given any to this point.

The description of time is subjective.  The measurement is objective.  A Martian "year" may not be the same as a Terran year, but that simply means that the 2 different locations are using a measuring stick with different markings and applying it to the SAME block of time.

No, Tavi did not age at a regular rate.  His mother stunted his growth through her furies.

Yes he aged just as anyone else did.  His growth was stunted.  Not his age.
 

I was just checking something for another thread and when I looked here, I'm wondering how often a wizard comes into the magic before the age of 10?  Based on the timeline, Carlos Ramirez was between 4 and 8 years old.  His birth is given as 16-19 BSF and the trial is between 11-12 BSF.  In DB Carlos seems to say that he was an apprentice at the time of Harry's trial.  (top of page 375 of the hardback)

I thought that most Wizards tended to initially manifest in the early teens (basically the same time as puberty kicks in), but I may just be imagining that.

Or was there a correction to Carlos' birth somewhere that I missed, maybe?  (or is this an unintentional slip in the book?)

He is not really the kind of guy to use New Pop culture lines.

Given where I am thinking the reference is coming from (The Godfather, if I am not mistaken) I would hardly call that a "new" pop culture line.