First off at age 28 you have probably missed the boat...age waivers exist but are unlikely as we are on short final to an era of massive cutbacks.

I think the Army National Guard has a higher age cutoff for helo pilots, I would look there.

If you want fixed wing you need to contact some units and see where they stand with age.

AD vs. Guard reserves is a much larger question than you seem to realize...

I would suggest AD only if you want to do that for a career (instead of airlines), or cannot get into the ANG. You can do about ten years (actually even 15) AD and then return to your airline with seniority intact (as though you never left). But I doubt you'll be able to make it to 20 years AD and keep your airline job, it has to do with the way the USERRA law is written. AD will involve occasional flying and full-time doing everything but flying (sometime for years with no flying). You will also need a masters degree to make it past about 12 years.

The ANG would be more a part-time gig where you keep your existing life and job (although it is a major time commitment, not to be taken lightly). ANG will involve more flying than AD.

At this point you need to get definitive answers on age limits so you know what's even possible. Age rules change with demand so I won't venture to guess exactly where things stand today, other than that you may be to old for most opportunities.