Can you accept a guy who is much younger than you??

Going to knock off at 7. Now just waiting for the clock to strike 7. My mind is totally blank now. Maybe have not recovered from staying out last night.
Back to east coast park yesterday afternoon to cycle after watching sunrise early in the morning. I also dunno where did I get the energy from to do tt, but i just dun want to stay at home. So decided to go cycling with my colleagues.
One of colleagues brought a guy with her and this guy is 5 years younger than her. I dunno whether are they already an item. They seemed very close but my colleague is still attached with a boyfriend (by the way also 5 years younger then her)!!. I personally find that their relationship is very unhealthy. Like some underground relationship.
The worst is that she sort of like using me as an excuse to go out with this guy. Whenever she goes out with him, she will tell her boyfriend that she is going out with me...., wats got to do with me.....
I dun think age is a problem but doing something unfaithful behind one's back is not acceptable.
Anyway, it is her life and is none of my business.