Children develop skills at different rates, but by 14 years most young people will:

Talk in longer sentences; usually 7-12 words or more.
Join sentences together using a range of joining words, such as ‘meanwhile’, ‘however’, ‘except’ so that they can explain more complicated ideas.
Be able to use sarcasm and know when others are being sarcastic to them.
Be able to change topics well in conversations.
Use more subtle and witty humour.
Show some understanding of idioms, such as “put your money where your mouth is!”.
Know that they talk differently to friends than to teachers. They are able to adjust the way they are talking easily depending on who they are talking to.
Understand and use slang terms with friends. They keep up with rapidly changing ‘street talk’.

Things to look out for:

Some young people struggle with speech and language development. Possible signs to look at for at this age include:

Difficulty giving specific answers or explanations.
Difficulty telling their ideas in the right order.
Better at understanding individual instructions than group instructions.
Your child finds it difficult to understand hidden meanings. For example, they wouldn’t understand that someone wants to close the window or turn up the heating when they say, ‘It’s a bit chilly in here!’.
Finding long and complicated instructions hard to understand.
Your child has trouble learning new words.
Your child takes a long time to organise what they are going to say or write.
Your child takes what others say literally. For example, they don’t understand that someone could take longer than one minute if they say, “I’ll be back in a minute”.
Your child has difficulty taking turns in conversations.
Your child talks to teachers and friends in the same way instead of adjusting their style of talking based on who they are talking to.