I can't make the same runs I did at 28, but I still want to be useful up front

As pace reduces, your movement can become more selective and more difficult to defend. You do not need to threaten twenty yards behind the centre-back every time. Start using shorter movements to move defenders: show towards the ball, pin one centre-back, drift onto the weaker defender, or arrive into the box after the first run has taken people away. Your hold-up play also becomes more valuable if you can connect the next attacker quickly rather than wrestling with the defender for too long. Secure the first contact, bring a teammate in, then move again. Inside the box, small movements matter. Losing a defender by a yard at the right time can be more useful than trying to win a sprint from ten yards away. You are not trying to play like your 28-year-old version more slowly. You are building a version of the role around what you now do best.