But people get very offended. The tension got so bad it resulted in a good friendship ending. My (now ex) friend Amanda screamed at me one night. "You don't like to go out, you don't like to party, you don't like to drink, you don't like to dance - what DO you like?" I thought about this for a few seconds. "Sitting." I replied. I enjoy sitting. And I enjoy thinking. Sitting and thinking. Even better: sitting and thinking at home.

This wasn't an activity we had in common.

Now that I'm nearly 40, I'm glad that the bar has been lowered.

Still, people need an excuse. 40 is a tricky age because you're old enough to get away with not going out, but not old enough to get away with not giving a reason. When I tell someone I don't want a late night the usual response is, "Oh, you must have to get up early for work, right?" Not really. Can't I just want to stay home?

A few weeks ago I was invited to a dinner party. "Plan to get here at eight or so," the hostess said, "We can all cook together."

I hesitated. "8pm?" She laughed. "Yes! Not 8AM!" Perhaps she hadn't heard the horror in my voice. Both options sounded incredibly unappealing.

I began the calculations. No one would get there on time, cooking wouldn't begin until nine, dinner wouldn't be served until 10 or 10:30. What kind of dinner party is that? We're not in Spain.

I'm not a late night person. By 11PM, I'm done. I have nothing left to say, the meagre social skills I have are depleted and tolerance levels for small talk dip below zero. The only excuse for beginning your evening at that time is if you're on drugs.

Or 17. Or, even better, 17 and on drugs. Other than that, I can't imagine it. Even if my house were to catch fire, I'd still have to consider if it was really worth getting out of bed and going out.

Chances are, this isn't going to change. I can't see turning 50 and suddenly making a plan to meet someone at midnight.

So now, I've learned to make friends with people who hate going out as much as I do. It's hard to meet people who I have this in common with though. Where do I meet them? We're always at home.

My friend Sam is similar. When we cancel plans, it's not a big deal. The other night she found a movie we both wanted to see but the only showing was 9:40pm.

It was Friday night so it might be sold out. Plus the thought of getting on the tube on a weekend night was a deterrent. And then sharing a cab home afterwards if we could even find one in Central London when the movie was over. I worried about that. By the time we were finished talking it through, we'd used up all of our energy. "Let's skip it," I said. "I'm exhausted."

But when you're older, people understand if you don't want to go to the later movie. And showing up isn't an issue; you don't have to explain. I can't wait. When I'm 80 I'll have a ready excuse: I'm old.