Am I too old for hostels at 28?
No — 28 is comfortably inside hostel range. The average hostel guest is mid-twenties and plenty are older; what actually changes with age isn't your welcome, it's your preferences. Most people drift from 12-bed dorms toward smaller dorms or private rooms in hostels — same social scene, better sleep.
Hostels aren't age-gated (a tiny number of party hostels set caps like 18–35, which tells you exactly what kind of week they're selling). The social spaces — kitchens, bars, walking tours, linkup events — are used by everyone from gap-year 18s to thirty-something career-breakers.
The honest shift at 28 is what you optimise for: privacy and sleep start beating the £4 saving of the biggest dorm. Private rooms in hostels are the underrated middle — hostel common areas and social energy, hotel-grade sleep.
If your actual question is "will I make friends", the answer tracks effort more than age: staying in social hostels, joining the events, and travelling in shoulder season when hostels are quieter but friendlier. Find your kind of trip.