To clarify, not a DCA - but after researching the process a few resources have helped with the "Black & White" programmatics vs. gouge/rumor/etc.
The link above is for all Commandant Instructions, notably CIM M1100.2F Recruiting Manual. Table 7-3 does a good job outlining the program overview, to include service obligation. For DCA applicants, a five year extended active duty contract. How you relate to the component is all Title 10, i.e. accepting a reserve commission. CIM 1000.3A Officer Accessions and CIM 3710.1H Air Operations Manual (essentially CG CNAF) have also been helpful.
To my understanding the age is waiverable. Based on program needs this has been fluid or rigid (like most programs).
Lastly, I've spoken with a lot of DCA or AD CG Pilots - I don't think having an MH-60 background necessarily weights your chances of staying within the airframe. That said, the CG has acquired additional MH-60 for conversion and fielding as the MH-65 reached airframe limitations (see Traverse City conversion for more details). The MH-65E is also being slowly fielded (assuming your a rotor guy).
Hope this helps!