18 month old not talking?

Yes you should be concerned. It's not normal for a child to not walk until 15 months mine started at 9 months. She is definately behind developmentally. A one year old should be making an attempt at talking. My daughter just turned two and knows 40 words and counts to ten. By one she was pointing and naming things. You should talk to your pediatrician she probably needs to see a specialist.