If you really want dart frogs I say go for it. Sometimes the worst advice you can give a person is to start with something other than what they really want "just to get some experience" Obviously if what someone really wants is a highly advanced species with very demanding requirements the advice may be sound but with dart frogs I would say that is not the case. I have found that D. leucomelas, D. auratus and D. t. azureus are some of the easiest species of frogs to keep and I would have no issues with recommending them to a first time frog keeper. As long as your do a bit of research first and make sure you meet their fairly easy to meet requirements I see no reason why you can't start off with dart frogs. Please note that I can only speak to the three species I mentioned above as they are the only ones I have kept (except some E. tricolors for a short time before I got rid of them) There may be others that would fit this category (I suspect there are several) but there may be others that are more demanding and may not.
One of the most overlooked aspect of a persons ability to care for a particular species is their desire to have that particular species. Even with some of the harder species if that is what they really want they may be willing to take that extra step or two to succeed. If they settle for a species that is "easier" but one they have no real affinity for they may fail simply because of a lack of interest.
About 12 years ago a customer came into my store with her son who wanted a ball python. That's all he wanted was a ball python but his mom said no. She was determined that if he was going to get a snake it would be something "easier" He settled for a corn snake and within 3 months she brought it back and said "I knew he wouldn't stay interested in it. A year or so later he turned 18, got his own apartment and one of the first things he bought was a ball python. Within 2 years he was breeding them and he still has his original snake and a nice collection of about a dozen or so morphs today.
My point is that as long as you can meet the care requirements and they are not an unreasonably difficult species I see no reason not to get what you really want.