"My older sister is twenty four years old."
That's incorrect, and it's hard to tell what you could be referring to.
Perhaps you're thinking of the question "你几岁？", which is used for asking young people how old they are. The issue isn't with "岁", it's with "几", which implies a relatively small number.
"毛泽东万岁", literally "Mao Zedong ten thousand years old", means "Long live Mao Zedong".
"年多" means "or more years". For example, "十年多" means "ten or more years". Perhaps you mixed this up with "你多大？", which is the way to ask an adult their age. They'll still respond with "岁".
These "no audio" comments aren't really productive. None of us can do anything about it.
You can try using the "report" function for the question, or you can submit a bug report.
That's what I was taught. Not that it's rude, per se, but rather perhaps overly formal and distant. I typed 我姐姐十二四岁, and it didn't accept my answer. On other questions where I've omitted the 的 with family members, it has accepted my answer. I'm not sure if it's a difference or just an oversight. Either way I'm going to report it so that the developers see it. This is a small course, and it's also very new. It's important that we report issues like this to the developers so that they can review it.