my son was 13 when his sister had her first baby so I'm much the same as you ,still looking after GC though the youngest is now 7 .Thats 40 years continuous childcare ,I went part time and job shared with my daughter when she went back to work after just a few weeks and had my first GD since she was two weeks old,walking down to the office for her breasfeeds.Number 3 GC I've had half of every week since she was just over a year when her parents split and now its all four for at least 3 days a week .I love having them ,they are brilliant kids ,this week we've been making christmas cakes as teacher presents ..they have loved decorating them and making the edible decorations .I dont THINK there will be another any time soon but I expect my son and his new partner will have at least one when they are ready...and I'll be here waiting to help with the care .