Old lizard Brumation?

Hello! So I’ve had my beardie for years now and every year without fail during late October to early November he goes inside his cave and well, I’m assuming goes into brumation. For the past few years I’ve left him alone, maybe given him some food once a week that he never comes out to eat. Now this has been fine for years but due to his old age (don’t know exact but we have guessed around 15) he hasn’t been eating as often as he used to, I’ve switched up feed, given him his favorite foods ect. But he’s just older and slower in general. This has caused him to lose some weight in the past year that I’ve been trying to get him to gain back (he’s already gained a bit back in this year and I was really happy with his progress). He isn’t horrible underwieght or anything but I am concerned about him not eating during the brumation period when he is already slightly underweight. Should I allow him to continue brumation and just continue with feedings whenever he is ready? Can anyone else with this old of beardies tell me any tips on this kind of thing? Ive been hand feeding him more recently to get him to gain weight which seems to work it’s just the brumation that really concerns me.