Pictures source: PINTEREST.COM
Many brands have vintage look test but it`s still not soft, Repeated wearing and washing is an another way, you will get there but it takes a long time. An easy way here, just follow the instructions and you get a well-worn t-shirt with vintage look.
If you want to get even more vintage look on your white or light colors tees, follow the same instructions but when it`s done poor some water in a bucket then poor black coffee or add some tea bags until the water is dark and let it work a day. Take the tees out and put them in the dryer but be aware It gives a good result but it won`t last for ever so you will have to do it again after a while.
Finally, You may also stretch them by holding the collar, use strength and you may cut the front part of the collar with scissors to get it even more vintage cool. see
Good luck folks !