imo, older people aren't interested in SERIOUS dating with someone much younger unless they're looking to corrupt. I guess there are special occasions, but most of the time the older person's quite aware of the age gap and any preconceived expectations of naivety.
By what I've witnessed, older individuals enjoy the sort of 'power'-like stance it gives them to date someone younger, almost like they're being looked up to or know more than the person they're dating.

Can actually see a lot of examples of it on tv or in movies.

As I said before, it's really up to the relationship, but if there are iffy feelings about the whole ordeal, chances are the relationship's not appropriate or it won't go anywhere.

4 years is barely an age gap by the time you're an adult.

I have an aunt and uncle with a 10 year age gap between them - when they got married she was 21 and he was 31 and they have had an extremely successful marriage and life together. There's also a 3 year age gap between my own parents (they were 23 and 26 when they married). And come to think of it, I know very few people who are in a relationship with someone the same age as them (or even just one year older or younger than them). But I think when you're in those "young adult" years, these things just feel like a bigger deal than they are.

I think with the specific ages mentioned in this poll, what makes it sound so much more overwhelming is the fact that one is in their teens while the other is in their twenties. I don't know if it's just me, but I feel like the age gap between a 24-year-old and a 20-year-old is less of an issue than the age gap between a 23-year-old and a 19-year-old. Which is ridiculous for obvious reasons! Let alone the fact that both partners are of consenting age in both examples, and that there's only a year difference between the examples, but also the actual age gap is exactly the same. It's just a psychological thing, I think, where being in your twenties makes you sound so much older than a 19-year-old.

So yeah, I don't think 4 years is anything to fret about really, but I can sympathise with the initial concern behind it because it feels like a bit of an age gap when you are young.