It entirely depends on whether or not the person lives selfishly for those 500 years. If they continue gaining and using experience they could be exceedingly productive.
If they sit around doing nothing but eating and playing video games, that would be a waste.
Productive at what? All of this assumes some grand human plan you can work at. Thus far the vast majority of "productive" humans are "productively" burning through resources with little value: our burn rate is ALREADY crazy with an upper cap on age.
If they sit around doing nothing but eating and playing video games, that would be a waste.