Sr. Citizen Taking Up Sport Again Questions, Please

Hello,

Haven't gone biking in probably 20 yrs, but would like to do a little,
again, for some light exercise.
Would have to be light, as am now in my 70's.

Have a 20 yr old, possibly more, Fuji bike.
Pretty much the regular, normal, looking style.
Road type, Not a Mountain bike style.
Think the frame is steel ?

The tires are the narrow road style.

Questions:

a. I can't read the psi inflation info on the side.
I seem to remember about 90 psi.
Does this sound about right.

b. The bike is really heavy. Steel frame, probably.

Are the new Road bikes, certainly not not "racing" bike styles,
meaningfully lighter ?

How about the Mountain Bike styles; significantly lighter ?

c. Guess I should also get a helmet.
Was in Sports Authority, and saw a Giro "Indicator" model for
about $ 35.
Is this a good brand ? The reviews in Amazon for the Indicator model
seem a bit mixed.

Would really want as light a weight as possible, and not any more than
about the $ 35.

Other suggestions, and opinions would be most appreciated ?

Much thanks,
Bob