to the OP: AmaurosisFugax, and anyone else wondering...
I am immediately suspicious of the motives and attitude of the person who made that comment to you. I've just passed the NCLEX (YAY!) at 40, 2 years earlier than my mother did. Before I went to nursing school, I had some HR experience, so I took a job in hospital HR for 18 months while I did my pre-reqs. Nurse Directors are the ones that hire nurses. The dozen+ nurse directors that I met during my time there all wanted experienced nurses, of course, and that makes sense. However, it was my understanding from all of them (ALL) that among new grad candidates, at least having some "Life Experience" is preferable.
Hospitals know they're making an investment in your real training to competency, but none are so foolish these days to assume you'll stick around for your 30-year career. For the time they have you, they want someone who is quick to learn, understands policy, understands policy doesn't cover everything, has good judgment, knows how to deal with difficult people, understands chain of command, and as another poster mentioned, doesn't bring drama and loads of family obligations to the job. If you've already raised your kids (mostly), figured out who you are, suffered personal losses, honored commitments, worked with others, etc, then you have experience that the kids just don't have, making you just as appealing, if not more so. The trick as an older worker is to make a point to appear energetic, and always interested to learn the latest technique/equipment/evidence-based-practice - avoid appearing stale or tired.
About grades - Figure it like this: when you're a kid, your brain works faster to retain things because there's less stuff in there. Now that you're older, you have more clutter in there; you have to discipline your mind a little more,and put more effort into retaining the info for recall & use. If you were an A student the last time you were in school, you will find it a little harder to get that A with the same amount of work. This is true no matter what kind of student you were, you will have to put out a little more effort to get the same result when getting started. HOWEVER - aren't you so much more sure this is what you want than you were at 20? Now that you're grown & setting this goal for yourself, your studies will be more meaningful, and you will WANT the info more than you did as a kid. I went to a CC program, finished in 18 months. Some of the A students were the kids, some were in their 30's, some were in their 40's, and my FAVORITE study partner and the safest student practitioner I know, is 53.
Consider - you walk into the patient's room, a 50 YO man with bladder irrigation after a prostate procedure (penile traction!). No matter how sophisticated your 20 YO classmates are, they will still be intimidated, and there will be awkwardness for them and for the patient. But when you walk in at 40, the patient assumes you've been a nurse for years (even though you're wearing a student uniform, uniforms vary so much these days, patients have trouble figuring it out). Your patient is less uncomfortable, so you can be more relaxed while you perform care. Think about it: most patients in hospital are older, and most older people feel they've learned a lot since 20, gained much and lost little. Therefore, patients will be more comfortable with an older nurse, leading to better outcomes.
Truly, it is a tradeoff, but if there is an imbalance, it is probably slightly in your favor. Go forward with confidence!
Yours in service,