Hello and welcome to eHealth Forum!

Normally the vaginal walls become loose with age. In your case since they are becoming tight, either there is fluid collection or the position of intercourse is such that it involves contraction of pelvic muscles making the vagina tighter with time.

If you have any symptoms such as low back ache or irregular menses or vaginal discharge, you could consult a gynecologist to rule out vaginal inflammation as a cause for tightness.

Hope this helps. Take care!