When did your baby learn to speak in full sentences?

My child is 14 months old now. He babbles gibberish at times but have also learnt to identify some people like his caregivers, papa, mama, yeye, etc. I realise we tried teaching him signs to which he does it when we say it without realising the meaning. Like he shakes his hand when we ask him if he doesn't want his food but he leans forward and opens his mouth. I'm wondering when will he realise the meaning of some of the words we are trying to teach him and articulate his thoughts more clearly..