The great advantage of an 18-19 year old is that because she's so inexperienced, her reactions are going to be fresh and spontaneous.
Spontaneity is a very valuable resource to have especially when you compare it to older WGs, who have been with so many men, that they've got everything down to a pat schedule and it's almost like a factory shift to them:
"DFK (tick), Mish (tick), 69 (tick), blowjob (tick), anal (tick)
and you have to keep up with them or risk upsetting the rhythm and she'll give you a look because you've upset her routine!
Barbie was one of the very worst in this respect.