First of all Chapter 61 retirement is a medical retirement. The term for a Guard retirement is a non regular retirement. In all circumstances you must agree to offset to a retirement to receive VA compensation and there is no scenario where it makes sense to not accept VA compensation since it is tax free. CRDP is the restoration of that offset by restoring and paying you for the pension that was originally offset by VA compensation.
If you are medically retired you will get the higher between your earned longevity pension from the Guard and your DOD% awarded by the PEB for unfitting conditions. Lets say your pension was $1,000 and your DOD% was 70% with your HIGH 3 base being $4,000. Your retirement rolls will show each computation and pick for you the higher amount. In this case 70% of $4,000 is $2,800. Since $2,800 is higher than $1,000 you get $2,800 for your chapter 61 retirement. Now lets say in either scenario you get $3,800 from VA compensation. When you filled out the application you DID NOT check the box for box 26 because you wanted the compensation and so are agreeing to have it offset any pension you have. See link to application here:
https://www.vba.va.gov/pubs/forms/vba-21-526ez-are.pdf So $3,800 VA is higher than $2,800. It's also higher than $1,000 so in either case you will only get $3,800 VA compensation + Tricare. You will not receive any money from your pension.
Now here is where it gets confusing for Soldiers. The most you can get for CRDP or CRSC is the combination of your earned longevity pension and your VA compensation. So if you are getting $3,800 from the VA and then later on qualify for CRSC or CRDP the most you can get is $1,000 earned pension from longevity AND $3,800. So the most the max compensation possible would be $4,800.
In your case since you can't get CRDP until you can apply for for your non regular retirement you should look into applying for CRSC after retiring if medically retired via chapter 61 retirement. There are a lot of presumptive conditions that are combat related if you have deployed to places such as Afghanistan, Kuwait or Iraq etc. My wife qualified for 80% CRSC which allowed her to max out compensation without needing to wait for getting her non regular retirement and all of her conditions were exposure related such as Asthma, Chronic Sinusitis, Tinnitus etc.
To answer your question if you are chapter 61 medically retired you are on PDRL and are retired. At age 60 you would qualify for your Guard retirement and apply for it and it would replace your chapter 61 retirement. Typically the non regular pension amount is less than their chapter 61 amount but when their non regular pension amount is combined with CRDP the total amount is higher than what they are getting with Chapter 61. My wife maxed out compensation with her chapter 61 retirement, + her pension (Her chapter 61 retirement amount was greater than the VA offset so she did get some compensation from her chapter 61 pension too). So she gets 3 seperate checks each month (Chapter 61 pension, VA compensation & CRSC) but when you total it up the amount is the same amount as she would be receiving from her non regular retirement and VA compensation via CRDP. Since CRSC is tax free she nets more compensation compared to CRDP since CRDP is the restoration of the pension offset by VA compensation. So if your pension is taxed then that CRDP restoration will be taxed.