A few questiony questions.

[Mr. woop woop]

1. If I use an ageing spell on a dragon like

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SANDS OF TIME
School necromancy; Level cleric 3, sorcerer/wizard 3, witch 3
Casting Time 1 standard action
Components V, S
Range touch
Target touched creature or object
Duration 10 minutes/level or instantaneous (see text)
Saving Throw none; Spell Resistance yes
You temporarily age the target, immediately advancing it to the next age category. The target immediately takes the age penalties to Strength, Dexterity, and Constitution for its new age category, but does not gain the bonuses for that category. A creature whose age is unknown is treated as if the spell advances it to middle age. Ageless or immortal creatures are immune to this spell.

If you cast this on an object, construct, or undead creature, it takes 3d6 points of damage + 1 point per caster level (maximum +15) as time weathers and corrodes it. This version of the spell has an instantaneous duration.

Will the dragon age and gain new HD(since HD and level are age based for dragons)? The wording makes it debatable, but still fun if you can abuse it.

2. My DM once told me, a while back, that you can't apply meta magic feats to a spell that would cause it to go over your max cast-able level. EVEN IF, the meta magic applied is then lowered by a feat or ability like arcane thesis.Is this true? Or can I take a spell to +200 spell level if I find a way to bring it back down?

3.Epic spells. Is there set levels? or is it, "As long as you can make the spell-craft dc, you can make the best spell you can think of!"?

[ketaro]

1) I personally hold to dragons being immortal as when was the last time you actually saw a dragon die of old age? Pff, nah; they've got a 100% adventurer casualty rate. (Or "I have no idea thats cheesy sir" )

2) Your DM is wrong. Things that reduce metamagic costs are not applied after the metamagic is applied to a spell. Its not [Prep Fireball in 3rd slot] -> [Apply Maximize, changing to 6th slot] -> [Apply metamagic reduction down to 4th slot].
The reduction in increased spell level for metamagic is constant whether the metamagic is applied to a spell or not. The reduction ability is not modifying the spell after metamagic is applied to it, it is modifying the actual metamagic feat so that a feat that added +3 to a spell's level will only add, say, +1 instead. You're not adding then subtracting and having the total effective spell level bouncing around like that.

3) Epic spells do not fall into any spell level. They simply require having the epic feat and making the spellcraft DCs/exp/gold requirements of crafting them and then the spellcraft DCs to cast them. Thus, you can't apply metamagic to them either.

There is an Epic feat that lets you unlock 10th level and higher spell slots, but those spell level slots are used simply for either prepping more lower level spells or for when you apply enough metamagic that you need slots above 9th for the spell(s).

[kitep]

1. Since the spell includes "witch 3", I suspect this is Pathfinder.  PF is mostly the same, but there are some differences, so you may want to mention this in future questions (most people add PF to the title).  As to whether it adds a HD to dragons, I'd say it's up to the DM.

2. Your DM is wrong on metamagic.  But since he's the DM, that makes him right 

3. There are no set levels to epic spells.  However, IIRC, you have to be an epic level character to take the epic feat that allows you to cast them, so 7th level characters can't do it even if they can make spell-craft 1000+.