64 years old and playing with bad knees and front shoulder.

Currently hitting TS1 IM with Nippon NS Pro Modus 3 Tour 120 in stiff.  7 iron is approx 150 yds.

Want to test lighter weight graphite in stiff in a TS3.  I have a TS3 7 iron with the same Nippon shaft and I like the strike feel better.

Is the weight drop too drastic?  Not expecting to get any better physically soon.

Opinions on the 2 shafts please.  Any other suggestions?  Have considered light weight steel also 105g.