Can you feel his cock and does it feel good inside you? If you can barely feel his cock then it's a size issue-you not tight enough or him not big enough.
If it's him not lasting long enough... I would say that 20 minutes is average for most men, and maybe even on the longer side for some guys. 20 minutes of thrusting can be quite a bit. Maybe you need him to go down on you longer.
Who are you talking to that can have sex for a long time? What amount of time are they talking about?
I think this brings out an interesting point.. I do feel his cock.. but i still feel i need tat feeling last for a long time... if 20 mins is average then y dont i get satisfied within 20mins.. is it just me or its the same feeling even for other women.. any girl to comment on this?