Consulting a nutritionist -- when, why, how?

[PamNY]

Lots of talk about nutritionists on this forum has made me curious. Why did you visit a nutritionist? How did you choose one? What credentials should they have (I can look up licensing requirements, if there are such, in my state, but of course I want to go beyond that)?

I don't have a specific problem to solve and I eat a very good diet, I think. My two questions are as follows. First, does being more active than average change my nutritional needs? I'm not an athlete and I don't go fast, but my cycling is consistent and mileage is increasing (probably 2,000 miles a year now). I also cycle in winter which feels like a strain on the body -- I don't know if it really is.

Second, how does aging change nutritional needs (if it does, and I wonder if this has even been studied in healthy people)?

Another issue -- I don't eat meat and want to give up eating fish, so I'd need someone who is knowledgeable about and supportive of a vegetarian diet.

I'm also very skeptical of fads/trends -- and if you don't understand this, wait until you are older. Everything you ever learned will have reversed itself a couple of times.

Any hints, tips, pitfalls, caveats, complaints, or success stories would be welcome.