My parents have also fostered for 15 years. They love it and still do it even though they're both pensioners. There is big HOWEVER coming though.
Not only is it hard work, 24/7, there are so many frustrations. You are treated like dirt by social services. This isn't social worker bashing, it's just even the good social workers have to put the rights of the kids against the rights of the parents, arrange contact/support for them, deal with courts which don't always make the wisest decisions, attend endless meetings ect. The foster carers are on the list after all of these other things are taken into account.
It's hard and sometimes heartbreaking work, but also very rewarding.
My parents started fostering via an agency. Pay was very good, much more support although much more damaged children. Now they're a bit older they prefer state fostering with more 'regular' kids-if such a thing exists.