I do UK to Australia every other year. I started in my early twenties and am now mid thirties. I've found jetlag has gotten worse as I've got older. I hardly felt it when I was 21! I'd say it takes about three days to be sleeping ok again now. My parents always take at least a week to recover.
Except this time. I had a six month old baby and jetlag felt completely the same as just being at home. :)