I agree with scalpel. I cant believe that

Don´t be ashamed of this...you are not alone! 

***

Gokuyum, may I ask if you don´t mind why did you edit this "short message" four times in 25 minutes?  

By the way, thank you for the link you gave, I went there and really got surprised to see the poor level of the contributors (I can´t believe they all are Turkish teachers!!!) May Allah protect our children from those teachers!!!

I think you decided to support me after seeing those guys´ incorrigible ignorance on Turkish grammar  da? nyet?

Thank you for asking this question..

No, I don´t say "1.80 boyundayım" but "1.75 boyundayım"  joking aside.. it is always "boyundayım"

Why? 

It is simple and clear..

"Ben 1.80 [metre boy-u]-n-da-y-ım" .. 

[metre boyu] is a noun compound..

So while the "metre" might not be there in word, it is there in meaning..

1.80 boyundayım..  

Likewise..

We say

75 kilo ağırlığındayım

[kilo ağırlığ-ı] is a noun compound

So there is no close relation between yaşımdayım and boyundayım/ ağırlığındayım

As Abla said the guilty is analogy 

"25 yaşımda, 1.80 boyunda, 75 kilo ağırlığındayım" => "25 yaşında, 1.80 boyunda, 75 kilo ağırlığındayım"

I think it is now totally clear..

I made some explanations on matter. But after reading previous posts I understood there was no need for further explanations and I deleted them.

You don´t need to be clear to me. I am clear and I am in "yaşındayım" camp. You´re totally confusing for learners.

25 yaş is a cardinal number (i.e. a quantity). If you want to say to be at/in something you need to use an ordinal number (birinci, ikinci, etc).

25 yaş = 25 years

25inci yaş = 25th year

25inci yaşımdayım = I am in my 25th year

If we talk about years we usually say

2000 yılı = year (of) 2000

or as in Azeri

2000inci yıl =2000th year

Similarly

25 yaşı = year of 25 (of someone)

or 25inci yaş  25th year (of someone)

So if you want to say you are 25 years old you either need to say

25 yaşı-n-dayım ( -n- = pronomial-n )

or

25inci yaş-ım-dayım ( -ım- = 1st sing. person possesive suffix )

 Thank you all for teaching Turkish, your devotion is extremely beautiful

Yet another example showing your ignorance about this type of usage.

"2000 yılı" is the short form of "miladi 2000 yılı" (miladi year of 200

miladi = miladın = of milat (Anno Domini A.D. )

The modifier is not 2000 but miladi..

When it comes to, for example, to "islam takvimi" (islamic/hijri calendar), not to cause a problem, we always use the word hicri

Hicri 1433 yılı (hijri year of 1433)

Don´t we?

That´s why they are always 3rd p.sing: yıl-ı

If it belonged to you, you would say "benim 2000 yılım"

If the root was "25 yaşı" as you claim,

we would say

"25 yaşı sendromu" but not "25 yaş sendromu" Right?

Here is what we say (according to the google search):

25 yaşı sendromu => 0 (ZERO)

25 yaş sendromu => 74.900

Open your eyes and look at it once more to see if it is "25 yaş" or "25 yaşı"..

Cardinal or pope or ordinal or whatever the modifier, an adjective compound is unsuffixed:

25 yaş

25inci yaş 

Why do you make "25 yaşı" look possible without 3rd.p. poss.adj "onun"?

This is what you know about "noun compounds"?

 If,by anology, a learner would say,

[25 yaşı]=>

25 yaşı sendromu

25 günü sonra

25 defası söyledim

I am sure you would give a long lecture about why they should be unsuffixed..

If, by analogy, a learner would say,

[Ben 25 yaşın(dayım)] =>Benim yaşın 25

You would teach them that it should always be: benim (noun)im 

But, if the learner would say,

Bu benim 25 yaşındaki resmim

You would say, CORRECT! 

And the learner, by analogy, would say,

Bu benim evindeki resmim

You would jump on your feet and scream, INCORRECT!

It is you who “are totally confusing for learners”

Is it really so hard for you to accept "yaşındayım" is grammatically incorrect?

Everything in a language should be grammatically correct?

You can say "xx yaşındayım" like most of us do, but you shouldn´t try to make it look grammatically correct.. I think the best way is to accept it as an exception..

"Grammatically correct" is a question of agreement. Learned (wo)men sit around a table, talk about it thoroughly and come to a decision. Probably it has happened in this case also and one of the forms has been recommended by language planners.

The learners are not children here. It is not a problem if teachers disagree about some details. To the opposite: I guess this thread has learned many of us something about compounds and numeric expressions. And every time we tell our age no matter how we do it we feel we are making an important decision...

Abla, I know you don´t mind, so I want to correct your (normally excellent) English.

"I guess this thread has learned taught many of us something about compounds and numeric expressions."

I also agree with your thoughts.

Sana katılıyorum 

I am not trying to make it correct or anything else. It´s what it is and I only tried to describe it and while doing it, I do not see any incorrectness in it.

I bet you also say "xx yaşındayım" at the times you do not make yourself force to use "xx yaşımdayım" form.