When we ST my DS he was about the same age. We used GW method and the first night, I sat on the floor right beside his bed and kept saying my phrase" it's bedtime M, lay down, Mummy is here". I also patted the mattress.
He cried and cried and what did the trick for me what to lay down on the floor with my back to him right beside his crib. Literally, the minute I did this, he must have thought, alright, she's here for the long haul. He laid down and went to sleep. 2+ hours the first night, second night, maybe 30 minutes, third night, maybe 5...
It works but you have to be so consistent and try hard to NOT engage them in conversation or react to thrown toys/loveys...just quietly replace and repeat you're phrase!
Good Luck!