I Am 62 Yrs. Old And Would Like To Keep

I am 62 yrs. old and would like to keep my levels like I was a 20 yr. old male. I was put on 200mg Testosterone cypionate im q week by my metabolic M.D. My G.P. now wants my to only take it once a month. Do Levels really change that much for a 160lb. male of my age on once monthly dosing