As GSM said, he's not implied to have weakened with age at all and as Kenshi said, he clearly wasn't capable of giving Roshi as much trouble as Goku did. The anime is the only place he presents actual feats in which he tanked BoDB Goku's attacks, yet was later staggered by a similar amount of bullets to what Bora endured which should place him below the last of the Mohicans Bora. He was also capable of destroying tanks with his physical strikes which is very impressive by the standards of early arc fighters. It was also suggested he was incapable of surviving a rocket launcher shell in the Piccolo Daimao filler, though that ought to be seen as expected when even Taopaipai was almost killed by a grenade.
Using anime feats, he ought to be at least on par with 21st TB top tiers such as Namu. His fighting style is one of just pure physical might, which would explain why he wasn't the type to cause someone as skilled as Roshi a lot of trouble (assuming they did spar). At most, and taking what I just said into account, he could potentially be far above 21st TB Goku, though still likely weaker than those of Taopaipai tier.
I'd probably lean more towards the low-end, considering he seemed in awe at the power of Roshi's Manly GAINZ mode, suggesting he'd only ever experienced what Base Roshi was capable of prior, with Roshi's power at the time likely not being much different to how it was in his introduction when taking into account Grandpa Gohan being born in Age 658.
