I Am 23 Years Old Can Putting a Retainer Now Push Back my Teeth After Having Removed an Anchor Tooth( Top Teeth)?

I removed one of my back teeth yesterday because needed to be removed. I have been told that now I must go and get a bridge to fill in the broken tooth. I was told by another doctor that i can put in a retainer and it will push back my teeth in about 6 months because my teeth are a little out,but the dentist that pulled out my tooth said that putting a retainer at this age might not work without first putting braces and at the age of 23 it will take alot more time than 6 months.I am not sure what to do