It's a new beginning and FUNtastic! Welcome "comebacker". I'm now 76 and had 3 lapses in playing, the first 40+years, and the 2nd and 3rd due to life threatening health and dental issues, the last resulting in a full upper denture and a lower partial (only 4 natural teeth remaining) thus only to say many here on TM have trod the same playground you now want to play on. Others, have presented some good concepts but whether or not you are in shape to follow them is entirely up to you. Weird as it may seem, I've suggesting you first swim and walk as much as you can to restore your overall strength and breath control.
Next set your metronome to 80 bpm or slower, your time signature to 4/4, with no sharps or flat notes and play linked whole notes (two measures) beginning with second line G then slur down to the F below and play two F whole notes linked, slur up to G again and repeat the G as you did before, but next slur up to the A above an play it for 2 linked whole notes and slur back to G and do the same again and slur back down to F continuing the same way for ten minutes and then rest for ten minutes. You could have breath marked anywhere at first, but try to lengthen the distance between breaths until you can do a set back to G. Add a note in each direction, higher and lower when you're ready to do so, but try. Next month try try using half notes, and the next quarters and so on until you're doing it with 16th notes, but remember that slur when you change notes. When your'e ready you'll add a sharp or flat to every note to form a chromatic scale. Keep swimming and walking.