If you feel the need for a 401K, then do it, if not who cares what parents, friends, brothers, sisters or any joe shmoe down the street thinks? Giving advice is one thing but nagging someone to do something, is on the level of really being controlling trying to make someone do something you think is best for them. No matter if the advice is sound or not, nagging removes the desire by the recipient to want to listen or follow directions.

Thing is, I'm guessing this is only one of the areas or times when your parents have nagged you about something they think is best for you.

Nod, say whatever you need to get the conversation to end and then just do what you feel is best for yourself. Clearly you're doing a good number of things right with a home of your own etc. So.. be confident in your own decisions and don't let people undermine that by their criticisms.