Are adult women too heavy to sit on a 14 year old boy's lap?

So I was with my brother, his wife, his son and daughter when they came to visit. We had to get in a car that only had 3 open seats due to stuff piled in it, so we had to double up on the two back seats. I had to let the son sit on my lap, but he said that he would prefer if I sat on his lap (in an "I don't want to sit on anyone's lap way", not a sexual way.

So anyways, I sat on his lap, and he made a little oof when I sat down. Since it is a car, I can't take off any weight with my legs (I weigh 163 pounds) and after 10 minutes he stopped talking to everyone, and he is usually the person to talk. After an hour we stopped for gas, and he asked if I could get up until we left. By the end of the ride, he was groaning. Was I too heavy for him? Don't teenage boys like it when a 23 year old woman will sit on their lap?
Are adult women too heavy to sit on a 14 year old boy's lap?
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