I don’t think promiscuity means having several consecutive sexual partners if they are committed relationships at the time.
I think it means having lots of one night stands.
I rented a bedsitter in 1969. The landlady gave me clear instructions - one boyfriend staying overnight was acceptable.
A parade of different ones wasn’t 
I really have no idea about what other people, young or old, get up to these days. But I’ve read that STDs have had a resurgence in the older generation.