Krissy Sins. She is definitely in her 20s, gives a fun half service session aswell.
Besides that I cant think of many independent providers who are in their 20s, and most of the ones listed as in their 20s or 30s are usually over 40.
I think some of the coco collective girls offer "massage" appointments aswell, im assuming those are only half service, you could look into that.
If you have the money to burn you can always pay a girls full service rate and just ask for half service.
Some massage parlour places have younger girls, I would have recommended Reach but all the threads on here reviewing them got taken down, so I dont go anymore