I think it is fine - I often tweak monsters to fit the level of the party.
I don't think it is and I would despise my DM for condescendingly giving me a fight with a dragon at level 4 (or 6) just to make me feel good about myself, but then again giving the players a fight is not exactly the point of the thread.
Why condescendingly - I do it to make a fun and interesting encounter. I'd suggest you try it some time - it really makes the game more fun and also helps avoid metagaming if you have players that are prone to doing that. Just last week I threw a modified Shambling Mound at a first level party which was a lot of fun for everyone involved.
The issue is the consistency of the presentation. Every time you have an adult red dragon in the game, it should be an adult red dragon, period.
I am not sure what you mean. If you are saying that every adult dragon should have the same stat block then I disagree - frankly it makes little sense considering dragons gain power throughout their lifetime. I'd rule that an adult dragon aged 101 is weaker than 800 year old.
