hmm, 10-20 minutes is probably pretty normal, some people can't even go for that long, but the thing is, its usually bad to compare to other people. When it comes to sex, the couple has to decide what is right for them since everyone else is different. I think "if it ain't broke, don't fix it." applies to your situation.
But you asked for suggestions,
some things I have heard is:
- Masturbate a few hours before so there is no urgency to go too fast.
(Also if a guy goes off early, if he is young and unselfish enough, he can usually keep on going with hands and such and be ready again in about 30 minutes and his lady will be flying from the ceiling by then)
- there is nothing wrong with a guy losing his woody for a short break, he can still be aroused anyway
(Tantric sex folks would tell you a guy needs to rest the bloodflow to his manhood every 30 minutes or so anyway)
- don't be too goal oriented about the orgasm part, don't worry about timing simultaneous orgasms or about performance. As said elsewhere, its about closeness and intimacy, the other things are bonuses.
- be in good physical shape. (weight) (Some people like morning romps better than nights because they are fresh in the morning)
- too much alcohol is a depressant and doesn't help men's bloodflow,
some say alcohol increases desire but reduces ability.
making love with clear heads, open eyes and lights on takes more trust.
- smoking is bad for the blood flow system as well.
Another thought is if there is other problems in a relationship, fixing the sex won't always help the other things, but the reverse does work, i.e. sometimes fixing the intimacy of the relationship does help the physical part.
In other words... talk about it.