When it starts being a job
The job you enjoy may have many overlooked drawbacks but are outweighed by benefits. I started on the ground floor and after twenty years, it was no longer fun. I took a generous retirement (before the days of 401K) that paid out immediately. I took the experience and formed a partnership that brought loads of clients and my own schedule. It still remains fun today another twenty five years later because I get to pick my clients. I have loaded a 401K to the max for me and my wife during that time. When you can save more than you spend, its hard to be discontent at your job but there are limits, some physical and some mental. Both capacities become less easy as the years pass but you have to know when to get out, pull the chute or whatever.
Keep Up with TechRepublic