[Grammar] I am going to be 15 years old next year.

[sitifan]

1. I will be 15 years old next year.
https://www.google.com/search?biw=1...c.1.64.psy-ab..0.1.83...33i10k1.0.qFygayhkkbI
2. I am going to be 15 years old next year.
https://www.google.com/search?biw=1...c.1.64.psy-ab..1.1.83...33i10k1.0.aeaqeYev3jc

I think #1 is correct. Is #2 also acceptable to native speakers?

 

[Rover_KE]

Yes – so is 'I'll be 15 next year'.

 

[Tdol]

There are many cases where will/be going to are interchangeable, and this is one.