I have a job and kids too. Last jam I (solo dev) was working late into every night (3AM) except one, where I fell asleep early from being extremley tired. I think the jam was 5 days long and at the end I was messed up from the lack of sleep. Jams get me so pumped up I can't stop gamedeving and forget time and sleep. I'm 40 now and it hits hard on my body especially when you need to be a good family member and worker by day. Still jams are alot of fun to me. I always make a game I'm proud of in a tiny time-frame. Also you gain a good load of XP. Deadlines are double-edged swords.
Just join one. What's the worst that can happen? You don't have to submit, when real life gets in the way. Everyone is different, own experience is gives you the best answer.