What are my options in US Military or civil services?

I am past 58, originally from India, a citizen of USA by domicile - first generation immigrant. Are there any areas where I can serve the military? A career in Air force, Navy, Army or Reserve full or part time is what I am interested. I am a mechanical engineer by profession, hold a bachelor degree, 25+ years of experience, presently working in private sector, healthy person, 5 1/2' not very heavily built. What are my options?