I started fell running in October 1984 and did a BG in July 1985. I was 21.
Ignore everyone else's goings on, and think about whether you want to do it and when.
Having 15 years fell running behind you isn't essential. Me and others show that.
Would have hated to be faced with squeezing a BG in and amongst racing, family, kids and work in my 30s/40s/50s. I have great respect for those who do manage this.
Do what suits you ZHR.