You are never too old,my Bass Brother. I was almost as old as you the first time around(37/38)and and now the big FOUR-EIGHT on my 2x as a beginner bassist.
If you are receiving formal lessons than you are
way ahead of the curve,sir.What does your instructor say about your progress? You should be able to confide in him with your concerns.Besides,you may be doing fine and dandy for your given situation,my friend,as most of us are ueber critical of our own efforts and/or abilities. Remember,learning and playing the bass guitar should be fun,enjoyable and an ongoing challenge(but in a positive way).If you aren`t having fun...at least for part of the time,then you`ll find it gets old in a hurry.
What lit the fire under me and made me feel like I was "playing" was just learning a few simple songs from tab.Notation is always the better option but sometimes for us rank ameutures it really pays dividends in our attitude and our bass esteem (my term there

). Baby steps,baby steps,baby steps...and you`ll be improving quicker than you realise.
Hang in there and make learning/playing FUN!
HosMan