I liked your story, and I don't think it's going to be your 'lone submission' for long. Oh, you forgot to include the link, so here it is for anyone else who's looking for a hot read.
'great opening sentence. 'great closing sentence, and plenty to keep the reader going in between.
I noted the following as I read your story:
undersexed Vinny
This didn't' sound quite right to me, maybe sex starved, or sexually frustrated Vinny? I mean this Vinny is a lot of things, but undersexed is not one of them.
...wondered Vinny to himself.
'to himself' is superfluous.
"Shit!" he exclaimed in an annoyed tone, "Who the hell can that be?"
No need for 'he exclaimed' or 'in an annoyed tone' the dialog says it all perfectly.
dirty thoughts creeping into his mind.
What dirty thoughts? You know every single reader, especially the male variety, who can use their own dirty little minds to think up something here, would like the details anyway.
"Yeah, I don't see why not." he answered...
I just bet his cock was 'answering' too. Again more details please.
..he turned onto his back and instructed her to ride him.
There's absolutely nothing wrong with this sentence, only it would have come to life more as dialog don't you think? Actually a few times I felt dialog would have worked better in your story, but maybe that's just me?
UUUUGGGGGHHHHHH!!!! OHHHHHHHHHH!!!!!"
Strings of consonants like this bug some people, personally, I couldn't care less one way or the other, but it's perhaps something to think about for future writing.
I think perhaps too your story could have been spit into a few more paragraphs. Each new dialog really needs a new line. It just makes it easier for the reader to follow.
"Sorry I took so long." He told her. "Just had a few things to tend to inside."
Considering what had gone happened upstairs, I thought this line was the sleaziest thing I have read in a long time. I loved it!! Lines like that just say it all don't they?
I thought you conveyed the dirty old man persona really well. I won't dare ask if you wrote this from experience, but I will say, I bet every man wish every eighteen year old girl was like this one.
Overall, it's probably not a story that will appeal to women much, but I am sure men will eat it right up.(No pun intended)
Congratuations on your very first submission to Literotica.
This woman loved it and would like to see more... It could have been a bit longer. I wanted to see is she came back begging for more, I know I would have.