It varies with each child. Both of my children were putting sentences together between ages 2 and 3. They spoke words long before that but full sentence responses, even though not 100% understandable were between ages 2 and 3.
My grandson is putting sentences together now and he is not quite 2 1/2. Some of his words are not real clear but after being around him for a while, you know what he is saying and when you respond to him properly, you see the expression on his face that you understood perfectly. He gets all excited then and will continue to talk.
An example of a sentence that I know what he is saying but some words are not exactly right is, "I want fruit snacks". His version of that sentence is "I want fruke nacks". It isn't perfect but it is easy to know what he means. Another one is when he says that he has to go to the potty. The sentence he is trying to say is, "I got to go potty". He will say, "I gotta go pottyot". For some reason he says the word potty with 3 syllables. For now, I don't see that as a problem. We keep saying the correct word to him and eventually he will say it right. The important thing is to acknowledge that he is talking and that he is understood. By speaking back to him in proper English will correct the incorrect pronunciations over time.
As long as you keep talking to the child the way you would talk to an adult, (minus bad language of course) the child will eventually pick up the correct words and put them together in proper sentences. To be sure that the child is on the right track and not having a learning problem, I would keep regular check ups with a Pediatrician so the progress can be monitored. Don't stress over hearing another kid talking better than you kid. They all learn at their own pace and it doesn't make them dumb or slow just because they seem like they might be behind another child near the same age. Relax!