Thanks for asking the query,
There are many reasons of retained decicous teeth even at the age of 19.
This can be due to hereditary problems, absence of tooth germ, impacted tooth
, trauma to the tooth germ while its formation.
I would suggest you to visit to an Orthodontist and get the checkup done.
Take an OPG radiograph.
A detailed clinical evaluation is needed to confirm the cause and plan appropriate treatment.
Sometimes Impacted tooth can be guided to errupt in the oral cavity with the help of surgery and braces.
If the wisdom tooth is not causing any problem dont worry about it.
Hope this helps out.