Which Japanese sentence is grammatically correct?

Question

My friend and I are making sentences from English to Japanese.

We are trying to turn this sentence into Japanese:

I think he's 23 years old, I'm not sure however.

We came up with:

思う彼は23歳。分かりませんだけど。

Omou kare wa 23sai. Wakarimasen dakedo.

and

思う彼は23歳だけど、分かりません。

Omou kare wa 23sai dakedo, wakarimasen.

Which of these sentences are grammatically correct? If both were wrong, what would be the correct way to say it in Japanese?

Answer 1

There are quite a few ways you could go about phrasing this, depending on the nuance/context, but pretty plainly:

彼は２３歳だと思うけど、わからない。 (lit. I think he is 23 years old, but I don't know.)

The 思う has to come at the end of the phrase; in your examples, it modifies the 彼, which would mean "he who thinks" or similar.