I placed 是 after 姐姐 and got wrong answer. I still want to know when to omit 是 in sentences.

我姐姐是二十四岁 what's wrong with this? Is not saying 的 here and saying 是 wrong? 是 feels a bit out of place.

”岁“ I find is most often used for very young people. I think “年多” is actually more accurate in this case.

the answer given is exactly as I wrote but I was marked wrong.....?

apparently i forgot to put a full stop at the end of the sentence, what? I've never had to do that & i can't do that

What's with the period being required? That never happened in Duolingo before. Particularly when it is not offered as a selection!

WHAT IS WITH THE PERIOD!

YOU DO NOT NEED THE EXTRA SYMBOL AT THE END

why 是 is not used after 姐姐？

why is 是 not used