Our Baxi is 28 years old and uses very little gas.
That's not a measure of efficiency.
The Baxi Solo 2 is a boiler from that era. It was 68% efficient.
Since 2018, all UK boilers have needed to be at least 92% efficient. Plenty are available at 94%. Some claim to be 97-98%.
You can google the efficiency of your specific boiler and work out the potential savings.
My annual gas consumption, averaged over 5 years:
New condensing boiler: 14470kWh
Old non-condensing boiler: 13972kWh
And have you investigated why?
Probably reasons are;
1) age. We all like our creature comforts more as we get older. Plus if you're lucky enough to retire) then you at home more, needing more heating.
2) Global pandemic! In the last 5 years we've had at least 2 years with significant restrictions on movement. This definitely pushes up your cnetral heating requirements. Many of us still don't go out quite as often as we used to.
If you think your gas consumption is still too high, get the central heating checked by a very good plumber (or a heating engineer). Efficiency gains are only achieved it the system has been designed correctly, with radiators and pipes sized accordingly. Balancing is v important, not just individually at each rad, but also with monitoring of the delta across the boiler (for several hours, in different weather conditions).