Your upper body is probably a lot heavier than it was at 17, causing you to put more weight on your hands in a forward riding position than you did then; plus you're not accustomed to the forward position so your trunk muscles (your "core") aren't sharing the load. Raising the bars and hoods slightly is an appropriate response.

Sliding the seat forward isn't necessarily helpful in this case since it moves your whole body centre of gravity forward relative to your feet and may tend to make you fall forward onto your hands. If you move it back to where it was, your butt kind of sticks out behind you and acts like a tyrannosaurus's tail, counterbalancing the frontal weight of your shoulders and head. Sheldon Brown explained this giving the example of a how you can't bend forward too far when your back is against a wall, without falling over, because you're prevented from shifting your butt back to compensate.