15 month old not talking only crying/rage

[gemzitab]

A little
Worries about my 15 month old son.
He doesn't say any words although understand a huge amount.
We try to cue him to talk but he just cries, but understands what we say.
He constantly cries and has meltdowns but won't say a word

Hates routine change and new things and people

When should
I worry?

Have a look at this from ICan. If you read all of it, at the bottom it tells you when to worry.

Have you thought of introducing some simple signs with him too? It may relieve the frustration. Managing is good as it's designed for children. Try things like milk, more, Mum, Dad and bed/sleep at first. Just sign them every time you say them.

When he's 16 months it might be worth seeing how he scores on the m-chat test too

Hard to know for sure from just a little description but I think it's really promising he understands things. It sounds possibly like there's a bit of a clash between his understanding of the world and his ability to communicate it (my LO has always been like this too, very behind with expressive language compared to receptive but EL is catching up now at 2) does he point? How about waving/clapping/copying actions to songs etc? I agree with PP about MCHAT and signing. The signing might just alleviate some of the frustration and help with the moods. Xx