If on ADOS orders for half a year and completed twenty years, can you enter the Army TAP program?

"Twenty years AFS and currently on ADOS" - Are you saying they did not apply for Sanctuary? That's an entirely different discussion.

All RC service members on orders of 180 days or greater are required to go through the mandatory portions of TAP (DOL briefing, VA benefits and services brief, etc.)

You might be confusing TAP with the Career Skills Program/SkillBridge program which do internships, apprenticeships, etc.

It's possible you are eligible for those programs. Per DoDI 1322.29*, the Service member must have completed at least 180 continuous days on active duty in the armed forces and is expected to be discharged or released from active duty within 180 days of starting the program. However, you're not entitled to participation in the program and the commander can say "No".

If this is what you were thinking of, read AR 600-18*, section 5-4 (Career Skills Program and Department of Defense SkillBridge program).
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* TAP components - https://www.dodtap.mil/dodtap/app/transition/gps
* DoDI 1322.29 - https://www.esd.whs.mil/Portals/54/Documents/DD/issuances/dodi/132229p.pdf
* AR 600-18 - https://skillbridge.osd.mil/docs/AR_600-81_Transition_Assistance_Program.pdf

MSG (Join to see) any suggestions for him?

You will need to contact the regional SFL-TAP manager.
And SFL-TAP is a 5 day program, it won't "finish the remaining time" of a six month order.