> I am sometimes tempted to tell colleagues "well I've done this professionally since before you were born, so..."

This sounds like you want the respect due to age alone.

The respect due to age alone is horrible. I wouldn't inflict it on my worst enemies.

The respect due to age and experience, on the other hand, is substantial, and something to strive for.

Back up your gray hairs :) with some relevant knowledge and the intelligent people will listen attentively.