We find it difficult, if not impossible, to market ourselves as a desirable candidate. We're not that good an actor.
I can totally relate to that way of thinking. That said, the feedback you've gotten is that you've been a good employee and a respected colleague. If the job counselor hasn't already suggested this, it should help to list some traits you generally possess that employers value, heck need, such as responsibility, accuracy, dependability, shows good judgment, loyalty, team player, etc. You can probably be objective about those example traits and others. You don't have to act, just present the facts.
My organization hires a whole range of ages, including plenty of people in their 40s, 50s and even 60s. The clear values are that it's easier to be sure of what you're getting from references, less ramp up time, and ironically, older employees individually may stay longer, often to retirement, providing work force stability. Hiring only young people in a lot of organizations isn't desirable, for many reasons.