I was going to suggest saying it's a matter of 'non-disclosure', but apparently that's not a real thing.

I would spin this one with a bit of back-story. Bring in a couple of key elements, emphasizing the value of independence and the struggle to stay on top.

The set-up works by establishing that you have an authoritarian figure in your life who always stood on their own two feet. Maybe a dad who built his business up from the poorhouse, or a grampa who kept the old farm independent when his neighbors sold out, whatever. The point of the story is going to be that out of respect for the these older, very important figures, it's important that you face life on your own terms. Succeed or fail, it's on you. That what you make is what you make, and what you don't is what you don't.

The hammer falls on the second act, the struggle, in which you are a young, enterprising young woman (I know I said it twice), just starting out, and it's important for you to be able to measure your success on your own terms and not someone else's. Obviously of course, you appreciate and admire the support around you, and look forward to sharing the experience of growth and doing well. But you have to measure yourself at the end of the day, and that means you need to know that you've made it by your own effort. Succeed or fail, it's all on you. Your previously mentioned authoritarian figure would be proud, and that's something special and important to you.

And that's the spin. You respect the hard work of your (older) co-worker, you appreciate the offer of support, but you have to do this own your own to make yourself and the people in your life proud of you. Thank the man for his kindness and thoughtfulness, but be firm that you're going to go your own way.

Everybody gets to feel warm and fuzzy, and you don't have to share a dime. And really, I think your <insert authoritarian figure> would have wanted it that way, don't you?