That don't sound like a lot of men.
I'm a guy, age 46 and I would guess over the last 30 yrs I have slept with maybe 100 woman. That averages out to 1 every 3.5 months.
Now mind you it hasn't been steady. Most of the sex I have had was mostly the same as you probably. From the ages of maybe 18-30. I would guess nearly 80% of the girls/woman I have slept with were between those ages.
Just hook ups from high school. Summertime flings. Woman at work. Etc,etc.
Not dealt interested in "relationships" during those years.
Then I got married when I was 30. Divorced a few years later so although the last 16 yrs have been slow, I still get my fare share. It's just now being older and divorced. Mortgage on a nice house.$100k per year job, responsibilites and no kids. I kinda yearn for something more "meaningful. And desire a partner and true love instead of just chasin skirts and tappin ass.
So no....I wouldn't think you were a "slut" at 28 with only sleeping with 50 guys.
But you might want to slow it down a bit. You don't want that pussy lookin like an arbys roast beef and cheddar any time to soon.