Rules look fine.
Chronomancer
See the flow needs to state what kind of action maintaining concentration is.
Move action, I think. Swift actions are how he casts spells.
Concentration on an ongoing effect is normally a standard action, although it's only actually defined for spells with concentration duration.
How does Chronological Security interact with someone else casting Time Stop?
Time Stop cast by a hostile caster wouldn't work against him. He'd act like those are normal rounds.
Strictly speaking,
Time Stop doesn't actually stop time, but rather speed it up for you to absurd amounts, like an amped up Haste. If you want Chronological Security to interact with that, you'd need to rewrite it (maybe to something like
Timeless Battlefield, which lets you join in on temporal displacement).
Life Span should say that you can't reduce your stats below 1 from age penalties.
Unless you're very odd, you wouldn't - the biggest penalty is -3 from Venerable. And if someone does do that? I'm not going to stop them.
Aging adjustments are cumulative, so Venerable is actually -6 Str/Dex/Con for +3 Int/Wis/Cha.
I agree with Strat on this one. If you've got low stats, there should be some older age categories you just can't operate at.
Siphon age should mention that the save iDC is the same for removing the negative levels after 24 hours, and also could use some text about how if a creature is killed by the negative levels they don't become undead.
There is no save after 24 hours. They save up front. Although I should make sure it doesn't allow undead.
Negative levels never last more than 24 hours (except for things like anarchic/axiomatic/holy/unholy weapons held by characters of opposed alignments, since they have special rules for it). After 24 hours, the negative level goes away, and you make a save against permanently losing a character level. This is in addition to and separate from the saving throw Siphon Age has to avoid gaining negative levels in the first place.
Temporal Discorporation - Normally this kind of class feature is a capstone. Is the DC based on the damage dealt by the killing attack or all of the damage you've taken?
Killing attack only.
Temporal Discorporation should probably be disabled for 1 day after you come back or something like that. Otherwise, unless you take a killing blow from a singular big hit (large enough to not auto-succeed on an Autohypnosis check), you can't actually die from hit point damage. Unlike
Fiery Discorporation, the ability has no cost, as a skill check you don't auto-fail on a natural 1 (skill checks are also a lot easier to pump to the stratosphere than saves, although that's a separate matter), and you regain hit points (Fiery Discorporation leaves you at whatever you were at before; it just negates the hit).
Assuming that issue is fixed, Fiery Discorporation is a 5th level discipline power (available by 9th level, or 12th with the Expanded Knowledge feat for non-Kineticists), so having a slightly stronger variation on it seems reasonable to me for a 13th level class feature.