My GE electric oven is not heating up to temperature.?

I set the temp for 500 degrees, the lower heating unit comes on, turns red, but then never gets close to the 500 degree setting. The unit is 17 years old and I've never had an problem with it. The controls are all electronic. Any ideas?|||Well had a similar problem with my GE double oven only when I heated it to 200 degrees it shot up to 500 and burned things really fast. That is the last time in years that I used the lower oven. Only used the top oven as it was not quite on the mark but close enough. We did buy a new double oven. The old GE would have cost over $350.00 to repair. That is almost half the cost of a brand new oven.The new one I bought is an Whirlpool Gold Accubake with the convection features. Love it and it is accurate.